Network Working Group J. Schlyter
Internet-Draft Kirei AB
Intended status: Informational S. Halen
Expires: 10 November 2025 The Swedish Internet Foundation
9 May 2025
Federated Authentication of Entities
draft-halen-fedae-01
Abstract
This document describes the Federated Authentication of Entities
(FedAE) framework, enabling secure machine-to-machine communication
within a federation. Both clients and servers perform mutual TLS
authentication, establishing trust based on a centrally managed trust
anchor published by the federation. Additionally, FedAE ensures
unambiguous identification of entities, as only authorized members
within the federation can publish metadata, further mitigating risks
associated with unauthorized entities impersonating legitimate
participants. This framework promotes seamless and secure
interoperability across different trust domains adhering to common
policies and standards within the federation.
Status of This Memo
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This Internet-Draft will expire on 10 November 2025.
Copyright Notice
Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Reserved Words . . . . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Diverse Design Patterns . . . . . . . . . . . . . . . . . . . 4
3. Trust Model . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Role of the Federation Operator . . . . . . . . . . . . . 5
3.2. Federation Members' Responsibilities . . . . . . . . . . 6
3.3. Chain of Trust . . . . . . . . . . . . . . . . . . . . . 6
3.4. Member Vetting . . . . . . . . . . . . . . . . . . . . . 7
3.5. Metadata Authenticity . . . . . . . . . . . . . . . . . . 8
4. Metadata Repository . . . . . . . . . . . . . . . . . . . . . 8
4.1. Metadata Submission . . . . . . . . . . . . . . . . . . . 9
4.2. Maintaining Up-to-Date Metadata . . . . . . . . . . . . . 10
5. Authentication . . . . . . . . . . . . . . . . . . . . . . . 11
5.1. Public Key Pinning . . . . . . . . . . . . . . . . . . . 11
5.1.1. Benefits of Public Key Pinning . . . . . . . . . . . 11
5.2. Pin Discovery and Preloading . . . . . . . . . . . . . . 12
5.3. Verification of Received Certificates . . . . . . . . . . 13
5.4. Failure to Validate . . . . . . . . . . . . . . . . . . . 13
5.5. Certificate Rotation: . . . . . . . . . . . . . . . . . . 13
5.6. Implementation Guidelines . . . . . . . . . . . . . . . . 14
6. Federation Metadata . . . . . . . . . . . . . . . . . . . . . 14
6.1. Federation Metadata claims . . . . . . . . . . . . . . . 15
6.1.1. Entities . . . . . . . . . . . . . . . . . . . . . . 16
6.2. Metadata Schema . . . . . . . . . . . . . . . . . . . . . 20
6.3. Example Metadata . . . . . . . . . . . . . . . . . . . . 20
6.4. Metadata Signing . . . . . . . . . . . . . . . . . . . . 21
6.5. Example Signature Protected Header . . . . . . . . . . . 22
7. Example Usage Scenarios . . . . . . . . . . . . . . . . . . . 22
7.1. Client . . . . . . . . . . . . . . . . . . . . . . . . . 24
7.2. Server . . . . . . . . . . . . . . . . . . . . . . . . . 24
7.3. SPKI Generation . . . . . . . . . . . . . . . . . . . . . 24
7.4. Curl and Public Key Pinning . . . . . . . . . . . . . . . 25
8. Deployments of the FedAE Framework . . . . . . . . . . . . . 25
8.1. Skolfederation Moa . . . . . . . . . . . . . . . . . . . 25
8.2. Swedish National Agency for Education . . . . . . . . . . 26
8.3. Sambruk's EGIL . . . . . . . . . . . . . . . . . . . . . 26
9. Security Considerations . . . . . . . . . . . . . . . . . . . 26
9.1. Security Risks and Trust Management . . . . . . . . . . . 26
9.2. TLS . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
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9.3. Federation Metadata Updates . . . . . . . . . . . . . . . 27
9.4. Verifying the Federation Metadata Signature . . . . . . . 27
9.5. Time Synchronization . . . . . . . . . . . . . . . . . . 27
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 27
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28
12. Normative References . . . . . . . . . . . . . . . . . . . . 28
13. Informative References . . . . . . . . . . . . . . . . . . . 28
Appendix A. JSON Schema for FedAE Metadata . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 33
1. Introduction
This document describes the Federated Authentication of Entities
(FedAE) framework, developed to complement multilateral SAML
federations, within the education sector. These federations often
rely on just-in-time provisioning, where user accounts are created at
first login based on information from the SAML assertion. However,
educators need to be able to manage resources and classes before
students access the service. FedAE bridges this gap by using secure
machine-to-machine communication, enabling pre-provisioning of user
information using a trust model and metadata structure inspired by
SAML federations.
FedAE is designed specifically for secure authentication in machine-
to-machine contexts, such as RESTful APIs and service-to-service
interactions, and is not intended for browser-based authentication.
Because its applicability in a browser environment has not been
studied, using FedAE within browsers is not recommended. Doing so
may introduce risks that differ from those typically addressed by
standard browser security models.
This work is not a product of the IETF, does not represent a
standard, and has not achieved community consensus. It aims to
address specific federation challenges and provide a framework for
secure communication.
1.1. Reserved Words
This document is an Informational RFC, which means it offers
information and guidance but does not specify mandatory standards.
Therefore, the keywords used throughout this document are for
informational purposes only and do not imply any specific
requirements.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
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1.2. Terminology
* Federation: A trusted network of entities that adhere to common
security policies and standards, using FedAE for secure
communication.
* Federation Member: An entity that has been approved to join the
federation and can leverage FedAE for secure communication with
other members.
* Federation Operator: The entity responsible for the overall
operation and management of the federation, including managing the
federation metadata, enforcing security policies, and onboarding
new members.
* Federation Metadata: A cryptographically signed document
containing information about all entities within the federation.
* Metadata Repository: A centralized repository storing information
about all entities within the federation.
* Member Metadata: Information about entities associated with a
specific member within the federation.
* Member Vetting: The process of verifying and approving applicants
to join the federation, ensuring they meet security and
trustworthiness requirements.
* Trust Anchor: The federation's root of trust is established by the
federation metadata signing key, which verifies the federation
metadata and allows participants to confidently rely on the
information it contains.
2. Diverse Design Patterns
FedAE is designed to be flexible and adaptable to the varying needs
of different federations. Federations can differ significantly in
terms of size, scope, and security requirements, which makes it
challenging to prescribe a one-size-fits-all trust framework and
security measures.
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For instance, in the European Union, the eIDAS (electronic
Identification, Authentication, and trust Services) regulation
establishes a framework for electronic identification and trust
services for electronic transactions within the EU. This regulation
provides a comprehensive set of standards for secure electronic
interactions across member states. National federations within EU
member states adhere to these standards, ensuring interoperability
and mutual recognition of electronic IDs across different countries.
Similarly, national federations, such as those found in education or
healthcare sectors, often have their own specific trust frameworks
and security measures tailored to their unique needs. These
federations may leverage existing national identification systems or
other trusted credentials to establish member identities and ensure
secure interactions.
Organizations may also set up their own federations, tailored to the
specific security requirements and trust models relevant to their
context. For example, a private business federation might establish
its own vetting processes and trust framework based on the nature of
its business and the sensitivity of the data being exchanged.
By allowing federations the flexibility to tailor their trust
frameworks and security measures, FedAE can support a wide range of
use cases. This flexibility is crucial for accommodating the diverse
requirements and challenges faced by different federations, ensuring
a secure and adaptable system for establishing trust and facilitating
secure communication.
3. Trust Model
The FedAE framework operates on a trust model that is central to its
design and functionality. This section outlines the key components
of this trust model and its implications for federation members and
the federation operator.
3.1. Role of the Federation Operator
The federation operator plays a critical role in the FedAE framework.
This entity is responsible for:
* Managing the central trust anchor, which is used to establish
trust across different domains within the federation.
* Vetting federation members to ensure they meet the required
standards and policies.
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* Maintaining and securing the federation metadata, which includes
public key pins [RFC7469], issuer certificates, and other
essential information.
Additionally, the federation operator SHOULD develop their own threat
models to proactively identify potential risks and threats. This
process involves examining the operating environment, evaluating both
internal and external threats, and understanding how vulnerabilities
can be exploited. The goal of the threat model is to enable the
federation operator to establish mitigation strategies that address
the identified risks.
The security and stability of the federation rely on the integrity
and competence of the federation operator. Members must be able to
fully trust this central authority, as its role is essential to
maintaining the federation's reliability and security.
3.2. Federation Members' Responsibilities
Federation members share the responsibility of maintaining trust and
security within the federation. Their responsibilities include:
* Adhering to the federation's security policies and procedures.
* Ensuring the accuracy and timeliness of their metadata
submissions.
* Cooperating with the federation operator's vetting and security
measures.
By fulfilling these responsibilities, federation members help sustain
the overall trust framework that enables secure and reliable
communication within the federation. Federation members submit
member metadata to the federation. Both the authenticity of the
submitted member metadata and the submitting member need to be
ensured by the federation.
3.3. Chain of Trust
Each federation operates within a trust framework that encompasses
its own security policies and procedures. This framework is designed
to ensure the integrity, authenticity, and confidentiality of
communications within the federation. Key components of this
framework include:
* Public key pinning [RFC7469] and preloading to thwart man-in-the-
middle attacks by ensuring validated certificates.
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* Regular updates and verification of federation metadata to prevent
the use of outdated or compromised information.
The federation operator aggregates, signs, and publishes the
federation metadata, which combines all members' member metadata
along with additional federation-specific information. By placing
trust in the federation and its associated signing key, federation
members trust the information contained within the federation
metadata.
The trust anchor for the federation is established through the
federation's signing key, a critical component requiring secure
distribution and verification. To achieve this, the federation's
signing key is distributed using a JSON Web Key Set (JWKS) [RFC7517],
providing a flexible framework for exposing multiple keys, including
the signing key and keys for rollover. This structured approach
ensures members can readily access the necessary keys for
verification purposes.
An additional layer of security is introduced through thumbprint
verification [RFC7638], where federation members can independently
verify the key's authenticity. This involves comparing the
calculated cryptographic thumbprint of the key with a trusted value,
ensuring its integrity. Importantly, this verification process can
be conducted through channels separate from the JWKS itself,
enhancing security by eliminating reliance on a single distribution
mechanism.
This trust framework is essential for enabling seamless and secure
interoperability across different trust domains within the
federation.
3.4. Member Vetting
To ensure the security and integrity of the FedAE framework, a member
vetting process is essential. Detailed vetting processes are beyond
the scope of this document but can be guided by established
frameworks such as eIDAS and eduGAIN.
The following are non-normative references to established frameworks:
* eIDAS: The eIDAS regulation establishes a framework for electronic
identification and trust services within the European Union. It
ensures secure and standardized electronic interactions across
member states, facilitating mutual recognition of electronic IDs.
Operators can refer to the eIDAS framework for guidance on robust
authentication and identity verification processes. See [eIDAS].
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* eduGAIN: eduGAIN is an interfederation service connecting identity
federations worldwide, primarily within the research and education
sectors. It ensures high standards of security and
interoperability, allowing institutions to collaborate seamlessly.
eduGAIN's processes for vetting can serve as a useful reference.
See [eduGAIN].
3.5. Metadata Authenticity
Ensuring the authenticity of metadata is crucial for maintaining the
security and trustworthiness of the FedAE framework. The specific
mechanisms for ensuring metadata authenticity are beyond the scope of
this document and must be defined by the federation or regulatory
bodies.
4. Metadata Repository
The FedAE metadata repository acts as a central vault, securely
storing all information about all participating federation members
and their respective entities. This information, known as federation
metadata, is presented as a JWS [RFC7515]to ensure its authenticity
and integrity.
The metadata repository is subject to stringent security measures to
safeguard the integrity of the stored information. This MAY involve:
* Member Management: The federation operator can centrally enforce
security policies and vet new members before they are added to the
repository.
* Access Controls: Only authorized members within the federation
should have access to the repository.
* Regular Backups: Robust backup procedures ensure data recovery in
case of unforeseen circumstances.
Before member metadata is added to the federation's repository, the
submitted metadata MUST undergo a validation process. This process
aims to verify the accuracy, completeness, and validity of the
information provided by a member. The validation process MUST
include, at a minimum but not limited to, the following checks:
* Format Validation: The system checks if the submitted metadata
adheres to the defined schema and format specifications.
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* Unique Entity ID: Checks are performed to ensure that the
entity_id in the submitted metadata is not already registered by
another member. Each entity within the federation must have a
unique identifier.
* Unique Public Key Pins: Public key pins [RFC7469] are used to
identify client entities within the federation metadata during the
connection validation process. When a server validates a client's
TLS connection, it extracts the pin from the client's TLS
certificate and matches it against entries in the federation
metadata. The requirements for pin uniqueness and usage are
detailed in Section Section 6.1.1.1.
* Certificate Verification: The issuer certificates listed in the
metadata are validated to ensure that the algorithms used in the
certificates are well-known and secure, and that the certificates
are currently valid and have not expired
* Tag Validation: Ensures that tags (see Section 6.1.1.1) in the
metadata adhere to the defined tag structure, verifying both
mandatory and optional tags. This process is crucial for
maintaining consistency and preventing unauthorized tags within a
federation.
The FedAE metadata repository serves as the vital foundation for
establishing trust and enabling secure communication within a FedAE
environment. By providing a central, secure, and controlled
repository for critical information, the metadata repository empowers
members to confidently discover other trusted entities, and establish
secure connections for seamless interaction.
4.1. Metadata Submission
It is up to the federation to determine which channels should be
provided to members for submitting their metadata to the metadata
repository. Members typically have the option to either upload the
metadata directly to the repository, provided such functionality
exists, or to send it to the federation operator through a designated
secure channel. If an insecure channel is used, additional measures
MUST be taken to verify the authenticity and integrity of the
metadata. Such measures may include verifying the checksum of the
metadata through another channel. The choice of submission channel
may depend on factors such as the federation's guidelines and the
preferences of the member.
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4.2. Maintaining Up-to-Date Metadata
In a FedAE federation, accurate and current metadata is essential for
ensuring secure and reliable communication between members. This
necessitates maintaining up-to-date metadata accessible by all
members.
* Federation Metadata: The federation operator publishes a JWS
containing an aggregate of all entity metadata. This JWS serves
as the source of truth for information about all members within
the federation. Outdated information in the JWS can lead to
issues like failed connections, discovery challenges, and
potential security risks.
* Local Metadata: Each member maintains a local metadata store
containing information about other members within the federation.
This information is retrieved from the federation's publicly
accessible JWS. Outdated data in the local store can hinder a
member's ability to discover and connect with other relevant
entities.
The following outlines the procedures for keeping metadata up-to-
date:
* Federation Operator Role: The federation operator plays a crucial
role in maintaining data integrity within the federation. Their
responsibilities include:
- Defining regulations for metadata management that MUST include,
at a minimum but not limited to, expiration and cache time
management.
- Implementing mechanisms to update the published federation
metadata, ensuring it adheres to the expiration time (exp, see
Section 6.4) and cache TTL (cache_ttl, see Section 6.1)
specifications.
* Member Responsibility: Members must follow the federation's
metadata management regulations and refresh their local metadata
store according to the defined expiration and cache regulations.
By adhering to these responsibilities, the Federation ensures that
information remains valid for the defined timeframe and that caching
mechanisms utilize up-to-date data effectively.
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5. Authentication
All communication established within the federation leverages mutual
TLS authentication, as defined in [RFC8446]. This mechanism ensures
the authenticity of both communicating parties, establishing a robust
foundation for secure data exchange.
5.1. Public Key Pinning
FedAE implements public key pinning as specified in [RFC7469].
Public key pinning associates one or more unique public keys with
each endpoint within the federation, stored in the federation
metadata. During a connection, clients and servers extract the
public key from the received certificate and validate it against the
pre-configured public key pins retrieved from the federation
metadata.
5.1.1. Benefits of Public Key Pinning
The decision to utilize public key pinning in the FedAE framework was
driven by several critical factors aimed at enhancing security and
ensuring trust:
5.1.1.1. Interfederation Trust
In interfederation environments, where multiple federations need to
trust each other, public key pinning remains effective. Each
federation can pin the public keys of entities in other federations,
ensuring trust across boundaries. Unlike private certificate chains,
which can become complex and difficult to manage across multiple
federations, public key pinning provides a straightforward mechanism
for establishing trust. FedAE interfederation addresses this
challenge by aggregating metadata from all participating federations
into a unified metadata repository. This shared metadata enables
secure communication between entities in different federations,
ensuring consistent key validation and robust cross-federation trust
and security.
5.1.1.2. Fortifying Security Against Threats
Public key pinning provides a robust defense mechanism by directly
binding a peer to a specific public key. This ensures that only the
designated key is trusted, preventing attackers from exploiting
fraudulent certificates. By eliminating reliance on external trust
intermediaries, this approach significantly enhances resilience
against potential threats.
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5.1.1.3. Use of Self-Signed Certificates
The use of self-signed certificates within the federation leverages
public key pinning to establish trust. By bypassing external CAs,
servers and clients rely on the federation's mechanisms to validate
trust. Public key pinning ensures that only the specific self-signed
public keys, identified by key pins in the metadata, are trusted.
5.1.1.4. Revocation
If any certificate in a certificate chain is compromised, the
revocation process can be complex and slow. This complexity arises
because not only the compromised certificate but potentially multiple
certificates within the chain might need to be revoked and reissued.
Public key pinning mitigates this complexity by allowing clients to
explicitly trust a specific public key, thereby reducing dependency
on the entire certificate chain's integrity.
If a leaf certificate is compromised within a FedAE federation, the
revocation process involves removing the pin associated with the
compromised certificate and updating the metadata with a pin from a
new certificate. This eliminates the need for traditional revocation
mechanisms and focuses the trust relationship on the specific,
updated public key.
5.2. Pin Discovery and Preloading
Peers in the federation retrieve these unique public key pins,
serving as pre-configured trust parameters, from the federation
metadata. The federation MUST facilitate the discovery process,
allowing peers to identify the relevant pins for each endpoint.
Information such as organization, tags, and descriptions within the
federation metadata supports this discovery.
Before initiating any connection, clients and servers MUST preload
the designated pins from the federation metadata. This aligns with
the principle described in Section 2.7 of [RFC7469], which introduces
optional sources for pinning information, with the federation
metadata serving as one such source. Preloading pins restricts
connections to endpoints with matching public keys, mitigating the
risks posed by fraudulent certificates.
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5.3. Verification of Received Certificates
Upon connection establishment, both endpoints, client and server,
must either leverage public key pinning or validate the received
certificate against the published pins. Additionally, the federation
metadata contains issuer information, which implementations MAY
optionally use to verify certificate issuers. This step remains at
the discretion of each individual implementation.
In scenarios where a TLS session terminates independent of the
application (e.g., via a reverse proxy), the termination point can
utilize optional untrusted TLS client certificate authentication or
validate the certificate issuer itself. Depending on the specific
implementation, pin validation can then be deferred to the
application itself, assuming the peer certificate is appropriately
transferred (e.g., via an HTTP header).
5.4. Failure to Validate
A received certificate that fails validation MUST result in the
immediate termination of the connection. This strict enforcement
ensures that only authorized and secure communication channels are
established within the federation.
5.5. Certificate Rotation:
To replace a certificate, whether due to expiration or other reasons,
the following procedure must be followed:
1. Publishing New Metadata: When a certificate needs to be changed,
federation members publish new metadata containing the pin
(SHA256 thumbprint) of the new public key. This ensures that the
new pin is available to all federation members.
2. Propagation Period: Allow time for the updated metadata to
propagate throughout the federation before switching to the new
certificate. This overlap period ensures that all nodes
recognize the new pin and avoid connection issues.
3. Switching to the New Certificate: After ensuring the new metadata
has propagated, members switch to the new certificate in their
TLS stack.
4. Removing Old Pin: After successfully switching to the new
certificate, members must publish updated metadata that excludes
the old pin. This final step ensures that only the current
public keys are trusted.
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5.6. Implementation Guidelines
Public key validation MUST always be enforced, either through direct
pinning or by deferring validation to the application.
For clients, public key validation typically occurs within the
application handling the TLS session, either by enforcing direct
pinning or by extracting and validating the public key against the
published pins.
For servers, validation depends on deployment. If the application
terminates the TLS session, it performs direct pinning or extracts
and validates the public key. If a reverse proxy terminates the TLS
session, it can enforce direct pinning or forward the certificate to
the application (e.g., via an HTTP header) for validation.
Implementations SHOULD, when possible, rely on libraries with native
support for pinning. Libcurl, for example, supports pinning via the
PINNEDPUBLICKEY option. In Python, the cryptography library can
extract public keys, while the requests package together with urllib3
can intercept certificates. Go provides crypto/tls and crypto/x509
for certificate inspection and public key extraction. In Java,
java.security.cert.X509Certificate enables public key extraction,
while java.net.http.HttpClient allows pinning enforcement using a
custom SSLContext and TrustManager. The choice of library is left to
the discretion of each implementation.
If bypassing standard CA validation is possible, it SHOULD be done.
If not, the issuers listed in the federation metadata MUST be used as
the trust store to validate certificate issuers while still enforcing
key pinning. Without issuer validation against issuers in metadata,
self-signed certificates would not be accepted. These mechanisms
ensure compatibility with existing TLS infrastructure while
maintaining strict security guarantees.
6. Federation Metadata
Federation metadata is published as a JWS [RFC7515]. The payload
contains statements about federation members entities.
Metadata is used for authentication and service discovery. A client
selects a server based on metadata claims (e.g., organization, tags).
The client then use the selected server claims base_uri, pins and if
needed issuers to establish a connection.
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Upon receiving a connection, a server validates the received client
certificate using the client's published pins. Server MAY also check
other claims such as organization and tags to determine if the
connections is accepted or terminated.
6.1. Federation Metadata claims
This section defines the set of claims that can be included in
metadata.
* version (REQUIRED)
Indicates the schema version of the federation metadata. This
ensures compatibility between members of the federation by
defining a clear versioning mechanism for interpreting metadata.
- Data Type: String
- Syntax: Must adhere to Semantic Versioning (https://semver.org
(https://semver.org)).
- Example: 1.0.0
* cache_ttl (OPTIONAL)
Specifies the duration in seconds for caching downloaded
federation metadata, allowing for independent caching outside of
specific HTTP configurations, particularly useful when the
communication mechanism isn't HTTP-based. In the event of a
metadata publication outage, members can rely on cached metadata
until it expires, as indicated by the exp claim in the JWS header
(see Section 6.4). Once expired, metadata MUST no longer be
trusted. If omitted, a mechanism to refresh metadata MUST still
exist to ensure the metadata remains valid.
- Data Type: Integer
- Syntax: Integer representing the duration in seconds.
- Example: 3600
* Entities (REQUIRED)
Contains the list of entities within the federation.
- Data Type: Array of Objects
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- Syntax: Each object MUST conform the entity definition (see
Section Section 6.1.1).
6.1.1. Entities
Metadata contains a list of entities that may be used for
communication within the federation. Each entity describes one or
more endpoints owned by a member. An entity has the following
properties:
* entity_id (REQUIRED)
A URI that uniquely identifies the entity. This identifier MUST
NOT collide with any other entity_id within the federation or
within any other federation that the entity interacts with.
- Data Type: URI
- Syntax: A valid URI.
- Example: "https://example.com"
* organization (OPTIONAL)
A name identifying the organization that the entity's metadata
represents. The federation operator MUST ensure a mechanism is in
place to verify that the organization claim corresponds to the
rightful owner of the information exchanged between nodes. This
is crucial for the trust model, ensuring certainty about the
identities of the involved parties. The federation operator
SHOULD choose an approach that best suits the specific needs and
trust model of the federation.
- Data Type: String
- Syntax: A name identifying the organization represented by the
entity.
- Example: "Example Org"
* issuers (REQUIRED)
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A list of certificate issuers allowed to issue certificates for
the entity's endpoints. For each issuer, the issuer's root CA
certificate MUST be included in the x509certificate property, PEM-
encoded. Certificate verification relies on public key pinning,
with the list of allowed issuers used only when a certificate
chain validation mechanism is unavoidable. For self-signed
certificates, the certificate itself acts as its own issuer and
MUST be listed as such in the metadata.
- Data Type: List of Objects
- Syntax: Each object contains a issuer certificate, PEM-encoded.
- Example: Issuer truncated for readability.
"issuers": [{
"x509certificate": "-----BEGIN CERTIFICATE-----\nMIIDDD"
}]
* servers (OPTIONAL)
Contains the list of servers within the entity.
- Data Type: Array of Objects
- Syntax: Each object MUST conform to the server definition (see
Section 6.1.1.1).
* clients (OPTIONAL)
Contains the list of clients within the entity.
- Data Type: Array of Objects
- Syntax: Each object MUST conform to the client definition (see
Section 6.1.1.1).
6.1.1.1. Servers / Clients
A list of the entity's servers and clients.
* description (OPTIONAL)
A human readable text describing the server or client.
- Data Type: String
- Syntax: Free-form text describing the server or client.
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- Example: "SCIM Server 1"
* base_uri (OPTIONAL)
The base URL of the server, which is required for endpoints that
describe server.
- Data Type: URI
- Syntax: A valid URL.
- Example: "https://scim.example.com/"
* pins (REQUIRED)
A list of objects representing Public Key Pins [RFC7469].
- Data Type: Array of Objects
- Syntax: A list of objects, where each object represents a
single public key pin with the following properties:
o alg (REQUIRED)
The name of the cryptographic hash algorithm. Currently,
the RECOMMENDED value is 'sha256'. As more secure
algorithms are developed over time, federations should be
ready to adopt these newer options for enhanced security.
+ Data Type: String
+ Syntax: The name of the algorithm.
+ Example: "sha256"
o digest (REQUIRED)
The public key of the end-entity certificate converted to a
Subject Public Key Information (SPKI) fingerprint, as
specified in section 2.4 of [RFC7469]. For clients, the
digest MUST be globally unique for unambiguous
identification. However, within the same entity_id object,
the same digest MAY be assigned to multiple clients.
+ Data Type: String
+ Syntax: SPKI fingerprint.
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+ Example: "+hcmCjJEtLq4BRPhrILyhgn98Lhy6DaWdpmsBAgOLCQ="
- Example:
"pins": [{
"alg": "sha256",
"digest": "+hcmCjJEtLq4BRPhrILyhgn98Lhy6DaWdpmsBAgOLCQ="
}]
* tags (OPTIONAL)
A list of strings that describe the endpoint's capabilities.
- Data Type: Array of Strings
- Syntax: Strings describing endpoint capabilities.
- Pattern: ^[a-z0-9]{1,64}$
- Example: ["scim", "xyzzy"]
Tags are fundamental for discovery within a federation, aiding
both servers and clients in identifying appropriate connections.
- Server Tags: Tags associated with servers are used by clients
to discover servers offering the services they require.
Clients can search for servers based on tags that indicate
supported protocols or the type of data they handle, enabling
discovery of compatible servers.
- Client Tags: Tags associated with clients are used by servers
to identify clients with specific characteristics or
capabilities. For instance, a server might only accept
connections from clients that support particular protocols. By
filtering incoming requests based on these tags, servers can
identify suitable clients.
Federation-Specific Considerations
While tags are tied to individual federations and serve distinct
purposes within each, several key considerations are crucial to
ensure clarity and promote consistent tag usage:
- Well-Defined Scope: Each federation MUST establish a clear
scope for its tags, detailing their intended use, allowed tag
values, associated meanings, and any relevant restrictions.
Maintaining a well-defined and readily accessible registry of
approved tags is essential for the federation.
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- Validation Mechanisms: Implementing validation mechanisms for
tags is highly recommended. This may involve a dedicated
operation or service verifying tag validity and compliance with
the federation's regulations. Such validation ensures
consistency within the federation by preventing the use of
unauthorized or irrelevant tags.
6.2. Metadata Schema
The FedAE metadata schema is defined in Appendix A. This schema
specifies the format for describing entities involved in FedAE and
their associated information.
Note: The schema in Appendix A is folded due to line length
limitations as specified in [RFC8792].
6.3. Example Metadata
The following is a non-normative example of a metadata statement.
Line breaks within the issuers' claim is for readability only.
{
"version": "1.0.0",
"cache_ttl": 3600,
"entities": [{
"entity_id": "https://example.com",
"organization": "Example Org",
"issuers": [{
"x509certificate": "-----BEGIN CERTIFICATE-----\nMIIDDDCCAf
SgAwIBAgIJAIOsfJBStJQhMA0GCSqGSIb3DQEBCwUAMBsxGTAXBgNV\nBAM
MEHNjaW0uZXhhbXBsZS5jb20wHhcNMTcwNDA2MDc1MzE3WhcNMTcwNTA2MD
c1\nMzE3WjAbMRkwFwYDVQQDDBBzY2ltLmV4YW1wbGUuY29tMIIBIjANBgk
qhkiG9w0B\nAQEFAAOCAQ8AMIIBCgKCAQEAyr+3dXTC8YXoi0LDJTH0lTfv
8omQivWFOr3+/PBE\n6hmpLSNXK/EZJBD6ZT4Q+tY8dPhyhzT5RFZCVlrDs
e/kY00F4yoflKiqx9WSuCrq\nZFr1AUtIfGR/LvRUvDFtuHo1MzFttiK8Wr
wskMYZrw1zLHTIVwBkfMw1qr2XzxFK\njt0CcDmFxNdY5Q8kuBojH9+xt5s
ZbrJ9AVH/OI8JamSqDjk9ODyGg+GrEZFClP/B\nxa4Fsl04En/9GfaJnCU1
NpU0cqvWbVUlLOy8DaQMN14HIdkTdmegEsg2LR/XrJkt\nho16diAXrgS25
3xbkdD3T5d6lHiZCL6UxkBh4ZHRcoftSwIDAQABo1MwUTAdBgNV\nHQ4EFg
QUs1dXuhGhGc2UNb7ikn3t6cBuU34wHwYDVR0jBBgwFoAUs1dXuhGhGc2U\
nNb7ikn3t6cBuU34wDwYDVR0TAQH/BAUwAwEB/zANBgkqhkiG9w0BAQsFAA
OCAQEA\nrR9wxPhUa2XfQ0agAC0oC8TFf8wbTYb0ElP5Ej834xMMW/wWTSA
N8/3WqOWNQJ23\nf0vEeYQwfvbD2fjLvYTyM2tSPOWrtQpKuvulIrxV7Zz8
A61NIjblE3rfea1eC8my\nTkDOlMKV+wlXXgUxirride+6ubOWRGf92fgze
DGJWkmm/a9tj0L/3e0xIXeujxC7\nMIt3p99teHjvnZQ7FiIBlvGc1o8FD1
FKmFYd74s7RxrAusBEAAmBo3xyB89cFU0d\nKB2fkH2lkqiqkyOtjrlHPoy
6ws6g1S6U/Jx9n0NEeEqCfzXnh9jEpxisSO+fBZER\npCwj2LMNPQxZBqBF
oxbFPw==\n-----END CERTIFICATE-----"
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}],
"servers": [{
"description": "SCIM Server 1",
"base_uri": "https://scim.example.com/",
"pins": [{
"alg": "sha256",
"digest": "+hcmCjJEtLq4BRPhrILyhgn98Lhy6DaWdpmsBAgOLCQ="
}],
"tags": [
"scim"
]
}],
"clients": [{
"description": "SCIM Client 1",
"pins": [{
"alg": "sha256",
"digest": "+hcmCjJEtLq4BRPhrILyhgn98Lhy6DaWdpmsBAgOLCQ="
}]
}]
}]
}
6.4. Metadata Signing
Federation metadata is signed using JWS and published using JWS JSON
Serialization according to the General JWS JSON Serialization Syntax
defined in [RFC7515]. Federation metadata signatures are RECOMMENDED
to be created using the algorithm _ECDSA using P-256 and SHA-256_
("ES256") as defined in [RFC7518]. However, to accommodate evolving
cryptographic standards, alternative algorithms MAY be used, provided
they meet the security requirements of the federation.
The following protected JWS header parameters are REQUIRED:
* alg (Algorithm)
Identifies the algorithm used to generate the JWS signature
[RFC7515], section 4.1.1.
* iat (Issued At)
Identifies the time at which the signature was issued. Its value
MUST be a number containing a NumericDate [RFC7519], section
4.1.6, although iat is typically used as a JWT claim, it is placed
here in the JWS header.
* exp (Expiration Time)
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Identifies the expiration time on or after which the signature and
federation metadata are no longer valid. The expiration time of
the federation metadata MUST match the value of exp. Its value
MUST be a number containing a NumericDate [RFC7519], section
4.1.4, and the claim is also placed in the JWS header, consistent
with this framework.
* iss (Issuer)
A URI uniquely identifying the issuing federation. This plays a
critical role in trust establishment within the FedAE framework.
The iss claim differentiates federations, preventing ambiguity and
ensuring that entities are recognized within their intended
context. Verification of the iss claim enables recipients to
determine the origin of the information and establish trust with
entities within the identified federation [RFC7519], section
4.1.1. The iss claim is registered for use as a JOSE header
parameter as per [RFC7519], section 5.3.
* kid (Key Identifier)
Identifies the signing key in the key set used to sign the JWS
[RFC7515], section 4.1.4.
Note: Although iss is registered for use in JOSE headers, iat and exp
are not. However, this specification explicitly places these values
in the protected JWS header to bind metadata validity information
directly to the signature. Implementers should be aware of this
usage and process these parameters accordingly.
6.5. Example Signature Protected Header
The following is a non-normative example of a signature protected
header.
{
"alg": "ES256",
"exp": 1707739718,
"iat": 1706875718,
"iss": "https://fedae.example.com",
"kid": "c2fb760e-f4b6-4f7e-b17a-7115d2826d51"
}
7. Example Usage Scenarios
The examples in this section are non-normative.
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The following example describes a scenario within the federation
"Skolfederation" where FedAE is already established. Both clients
and servers are registered members of the federation. In this
scenario, clients aim to manage cross-domain user accounts within the
service. The standard used for account management is SS 12000:2018
(i.e., a SCIM extension).
+---------------------------------------------+
| |
| Federation Metadata |
| |
+---+--------------------------+--------------+
| |
(A) (A)
| |
v v
+---+----+ +------------+--------------+
|Local MD| | Local MD |
+---+----+ +----+------------- ---+----+
| | |
(B) (C) (F)
| | |
v v v
+---+----+ +----+---+ +----+---+
| | | | | |
| Client | | Reverse| | App |
| +--(D)-->+ Proxy +--(E)-->+ |
| | | | | |
| | | | | |
+--------+ +--------+ +--------+
A. Entities collect member metadata from the federation metadata.
B. The client pins the server's public key pins.
C. The reverse proxy trust anchor is setup with the clients'
certificate issuers.
D. The client establishes a connection with the server using the
base_uri from the federation metadata.
E. The reverse proxy forwards the client certificate to the
application.
F. The application converts the certificate to a public key pin and
checks the federation metadata for a matching pin. The entity's
entity_id should be used as an identifier.
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7.1. Client
A certificate is issued for the client and the issuer is published in
the federation metadata together with the client's certificate public
key pins
When the client wants to connect to a remote server (identified by an
entity identifier) the following steps need to be taken:
1. Find possible server candidates by filtering the remote entity's
list of servers based on tags.
2. Connect to the server URI. Include the entity's list of
certificate issuers in the TLS clients list of trusted CAs, or
trust the listed pins explicitly.
3. If pinning was not used, validate the received server certificate
using the entity's published pins.
4. Commence transactions.
7.2. Server
A certificate is issued for the server and the issuer is published in
the federation metadata together with the server's name and
certificate public key pin.
When the server receives a connection from a remote client, the
following steps need to be taken:
1. Populate list of trusted CAs using all known entities' published
issuers and required TLS client certificate authentication, or
configure optional untrusted TLS client certificate
authentication (e.g., optional_no_ca).
2. Once a connection has been accepted, validate the received client
certificate using the client's published pins.
3. Commence transactions.
7.3. SPKI Generation
Example of how to use OpenSSL to generate a SPKI fingerprint from a
PEM-encoded certificate.
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openssl x509 -in <certificate.pem> -pubkey -noout | \
openssl pkey -pubin -outform der | \
openssl dgst -sha256 -binary | \
openssl enc -base64
7.4. Curl and Public Key Pinning
Example of public key pinning with curl. Line breaks are for
readability only.
curl --cert client.pem --key client.key --pinnedpubkey 'sha256//0Ok
2aNfcrCNDMhC2uXIdxBFOvMfEVtzlNVUT5pur0Dk=' https://host.example.com
8. Deployments of the FedAE Framework
The FedAE framework has proven its practical value and robustness
through successful deployments in several environments.
8.1. Skolfederation Moa
Skolfederation Moa [Moa], is a federation designed to secure
communication between digital educational resources and schools.
FedAE is developed to meet Moa's needs and enables secure data
exchange for schools, municipalities, educational platforms, and
services across Sweden.
The community plays a crucial role in this type of federation.
Members are active participants, and the FO ensures the federation
runs smoothly and serves their needs. Moa's success highlights the
importance of collaboration, with members and the FO working together
to maintain trust, security, and interoperability in the education
sector.
The deployment of FedAE in the Swedish education sector has provided
several key insights. Maintaining an accurate registry of metadata
ownership with reliable contact information is essential for
troubleshooting and ensuring accountability. The deployment also
demonstrated the importance of setting reasonable expiration times
for metadata. Too short an expiration can hinder the ability to
implement contingency plans for publishing new metadata during
outages.
Metadata validation is necessary to maintain a stable federation.
While manual validation may be sufficient in the early stages of a
federation, it becomes unmanageable as the federation scales.
Without an automated validation process, incorrect metadata uploaded
by members is likely to go undetected, leading to publication of
incorrect metadata.
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The signing key is needed to sign metadata. Under fallback
scenarios, even if metadata can be retrieved from elsewhere, without
access to the signing key, it is impossible to publish metadata.
Therefore, secure and redundant management of the signing key is
crucial to enable fallback mechanisms and ensure reliable signing and
distribution of metadata. If metadata is retrieved from a location
other than the official repository, it is mandatory to validate its
signature to maintain trust and ensure the authenticity of the
metadata.
8.2. Swedish National Agency for Education
The Swedish National Agency for Education [SkolverketFedAE] leverages
FedAE within its digital national test platform to establish a robust
authentication mechanism. The platform utilizes an API for client
verification prior to secure data transfer to the agency's test
service, ensuring the integrity and confidentiality of educational
data.
8.3. Sambruk's EGIL
Sambruk's EGIL [EGIL], a platform providing digital services to
municipalities, has successfully integrated the FedAE framework.
This deployment demonstrates the framework's adaptability to support
a wide range of digital service infrastructures.
These deployments highlight the effectiveness of the FedAE framework
in enhancing security and interoperability within the educational
sector.
9. Security Considerations
9.1. Security Risks and Trust Management
The security risks associated with the FedAE framework are confined
to each individual federation. Both the federation operator and
federation members share the responsibility of maintaining trust and
security within the federation. Proper handling and management of
metadata, as well as thorough vetting of federation members, are
crucial to sustaining this trust and security. Each federation
operates within a trust framework, which includes its own security
policies and procedures to ensure the integrity and reliability of
the federation.
9.2. TLS
The security considerations for TLS 1.3 [RFC8446] are detailed in
Section 10, along with Appendices C, D, and E of RFC 8446.
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9.3. Federation Metadata Updates
Regularly updating the local copy of federation metadata is essential
for accessing the latest information about active entities, current
public key pins [RFC7469], and valid issuer certificates. The use of
outdated metadata may expose systems to security risks, such as
interaction with revoked entities or acceptance of manipulated data.
9.4. Verifying the Federation Metadata Signature
Ensuring data integrity and security within the FedAE framework
relies on verifying the signature of downloaded federation metadata.
This verification process confirms the data's origin, ensuring it
comes from the intended source and has not been altered by
unauthorized parties. By establishing the authenticity of the
metadata, trust is maintained in the information it contains,
including valid member public key pins and issuer certificates. To
achieve a robust implementation, it is crucial to consider the
security aspects outlined in [RFC7515]. Key points include handling
algorithm selection, protecting against key compromise, and ensuring
the integrity of the signature process.
9.5. Time Synchronization
Maintaining synchronized clocks across all federation members is
critical for the security of the FedAE framework. Inaccurate
timestamps can compromise the validity of digital signatures and
certificates, hinder reliable log analysis, and potentially expose
the system to time-based attacks. Therefore, all federation members
MUST employ methods to ensure their system clocks are synchronized
with a reliable time source.
10. Acknowledgements
This project was funded through the NGI0 PET Fund, a fund established
by NLnet with financial support from the European Commission's Next
Generation Internet programme, under the aegis of DG Communications
Networks, Content and Technology under grant agreement No 825310.
The authors would like to thank the following people for the detailed
review and suggestions:
* Rasmus Larsson
* Mats Dufberg
* Joe Siltberg
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* Stefan Norberg
* Petter Blomberg
The authors would also like to thank participants in the EGIL working
group for their comments on this specification.
11. IANA Considerations
This document has no IANA actions.
12. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC7469] Evans, C., Palmer, C., and R. Sleevi, "Public Key Pinning
Extension for HTTP", RFC 7469, DOI 10.17487/RFC7469, April
2015, <https://www.rfc-editor.org/info/rfc7469>.
[RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
2015, <https://www.rfc-editor.org/info/rfc7515>.
[RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517,
DOI 10.17487/RFC7517, May 2015,
<https://www.rfc-editor.org/info/rfc7517>.
[RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<https://www.rfc-editor.org/info/rfc7519>.
[RFC7638] Jones, M. and N. Sakimura, "JSON Web Key (JWK)
Thumbprint", RFC 7638, DOI 10.17487/RFC7638, September
2015, <https://www.rfc-editor.org/info/rfc7638>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
13. Informative References
[EGIL] Sambruk, "EGIL - manage your school's digital user
accounts efficiently", 2022,
<https://sambruk.se/egil-dnp/>.
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[Moa] The Swedish Internet Foundation, "Machine and Organization
Authentication", 2022,
<https://wiki.federationer.internetstiftelsen.se/x/
LYA5AQ>.
[RFC7518] Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
DOI 10.17487/RFC7518, May 2015,
<https://www.rfc-editor.org/info/rfc7518>.
[RFC8792] Watsen, K., Auerswald, E., Farrel, A., and Q. Wu,
"Handling Long Lines in Content of Internet-Drafts and
RFCs", RFC 8792, DOI 10.17487/RFC8792, June 2020,
<https://www.rfc-editor.org/info/rfc8792>.
[SkolverketFedAE]
Swedish National Agency for Education, "Authentication API
for User Management", 2023,
<https://github.com/skolverket/dnp-
usermanagement/blob/main/authentication-api/README.md>.
[eIDAS] European Commission, "eIDAS: electronic Identification,
Authentication and trust Services", 2014,
<https://eidas.ec.europa.eu/>.
[eduGAIN] GEANT Association, "eduGAIN: Interfederation service
connecting research and education identity federations
worldwide", 2023, <https://edugain.org>.
Appendix A. JSON Schema for FedAE Metadata
This JSON schema defines the format of FedAE metadata.
Version: 1.0.0
=============== NOTE: '\\' line wrapping per RFC 8792 ===============
{
"$schema": "https://json-schema.org/draft/2020-12/schema",
"$id": "https://fedae.se/schema/fedae-metadata-schema.json",
"title": "JSON Schema for Federated Authentication of Entities",
"description": "Version: 1.0.0",
"type": "object",
"additionalProperties": true,
"required": [
"version",
"entities"
],
"properties": {
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"version": {
"title": "Metadata schema version",
"description": "Schema version follows semantic versioni\
\ng (https://semver.org)",
"type": "string",
"pattern": "^\\d+\\.\\d+\\.\\d+$",
"examples": [
"1.0.0"
]
},
"cache_ttl": {
"title": "Metadata cache TTL",
"description": "How long (in seconds) to cache metadata.\
\ Effective maximum TTL is the minimum of HTTP Expire and TTL",
"type": "integer",
"minimum": 0,
"examples": [
3600
]
},
"entities": {
"type": "array",
"items": {
"$ref": "#/$defs/entity"
}
}
},
"$defs": {
"entity": {
"type": "object",
"additionalProperties": true,
"required": [
"entity_id",
"issuers"
],
"properties": {
"entity_id": {
"title": "Entity identifier",
"description": "Globally unique identifier for t\
\he entity.",
"type": "string",
"format": "uri",
"examples": [
"https://example.com"
]
},
"organization": {
"title": "Name of entity organization",
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"description": "Name identifying the organizatio\
\n that the entity's metadata represents.",
"type": "string",
"examples": [
"Example Org"
]
},
"issuers": {
"title": "Entity certificate issuers",
"description": "A list of certificate issuers th\
\at are allowed to issue certificates for the entity's endpoints. Fo\
\r each issuer, the issuer's root CA certificate is included in the \
\x509certificate property (PEM-encoded).",
"type": "array",
"items": {
"$ref": "#/$defs/cert_issuers"
}
},
"servers": {
"type": "array",
"items": {
"$ref": "#/$defs/endpoint"
}
},
"clients": {
"type": "array",
"items": {
"$ref": "#/$defs/endpoint"
}
}
}
},
"endpoint": {
"type": "object",
"additionalProperties": true,
"required": [
"pins"
],
"properties": {
"description": {
"title": "Endpoint description",
"type": "string",
"examples": [
"SCIM Server 1"
]
},
"tags": {
"title": "Endpoint tags",
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"description": "A list of strings that describe \
\the endpoint's capabilities.",
"type": "array",
"items": {
"type": "string",
"pattern": "^[a-z0-9]{1,64}$",
"examples": [
"xyzzy"
]
}
},
"base_uri": {
"title": "Endpoint base URI",
"type": "string",
"format": "uri",
"examples": [
"https://scim.example.com"
]
},
"pins": {
"title": "Certificate pin set",
"type": "array",
"items": {
"$ref": "#/$defs/pin_directive"
}
}
}
},
"cert_issuers": {
"title": "Certificate issuers",
"type": "object",
"additionalProperties": false,
"properties": {
"x509certificate": {
"title": "X.509 Certificate (PEM)",
"type": "string"
}
}
},
"pin_directive": {
"title": "RFC 7469 pin directive",
"type": "object",
"additionalProperties": false,
"required": [
"alg",
"digest"
],
"properties": {
Schlyter & Halen Expires 10 November 2025 [Page 32]
Internet-Draft FedAE May 2025
"alg": {
"title": "Directive name",
"type": "string",
"enum": [
"sha256"
],
"examples": [
"sha256"
]
},
"digest": {
"title": "Directive value (Base64)",
"type": "string",
"pattern": "^(?:[A-Za-z0-9+/]{4})*(?:[A-Za-z0-9+\
\/]{2}==|[A-Za-z0-9+/]{3}=)?$",
"examples": [
"HiMkrb4phPSP+OvGqmZd6sGvy7AUn4k3XEe8OMBrzt8\
\="
]
}
}
}
}
}
Authors' Addresses
Jakob Schlyter
Kirei AB
Email: jakob@kirei.se
Stefan Halen
The Swedish Internet Foundation
Email: stefan.halen@internetstiftelsen.se
Schlyter & Halen Expires 10 November 2025 [Page 33]