EIDA AAI based on B2ACCESS OAuth2.0 (Draft)

Introduction

Implementing federated restricted data access for EIDA Web-Services based on the contemporary FDSNWS Specifications (Version 1.1b) (i.e. HTTP Digest authentication RFC2617) is not possible: User credentials are hashed before being passed from a client to eida-federator/fdsnws-dataselect/queryauth and consequently cannot be restored and reused for accessing EIDA endpoints (i.e. eida-endpoint/fdsnws-dataselect/queryauth) to be federated.

Protected resources of SeisComp3 FDSNWS instances currently implement restricted data access both by means of HTTP Digest authentication and a token based authentication mechanism. Due to the original requirement to stick to the current FDSNWS standard the implementation is based on:

EUDAT B2ACCESS (federated identities e.g. eduGAIN) SAML2.0 token based authorization,
a custom client service implementation wrapping the SAML2.0 tokens issued by B2ACCESS into a custom token format,
a custom access token format based on a PGP ASCII-armored, digitally signed JSON object
and an additional /auth resource for EIDA-ERS instances.

Henceforth, accessing a protected resource is implemented following a three-step approach:

The client has to retrieve an access token from the issueing service (if no valid token available)
The client has to transmit the access token using the service’s /auth resource; the web-service then returns FDSNWS standard conform access credentials
The client uses those access credentials to access the protected resource (i.e. the /queryauth resource)

It is correct that a token based AAI mechanism much better fulfills the requirements of a federated FDSNWS environment. Unfortunately, the solution has a few shortcomings:

From the client’s point of view, the approach is not straight forward to use: It is a 3-step procedure to retrieve the token, retrieve service credentials, and use the service. All done using different technology, and at different time scales.
The token combines confirmation of identity and confirmation of access rights. It replaces the user in any respect, and cannot be revoked. As the token issueing process cannot be automated, lifetimes of weeks to months are envisaged for these tokens, which is a major security concern.
Within a distributed service environment such as EIDA the approach requires EIDA gateway resource servers (e.g. EIDA Federator) to manage tokens in order to issue requests to endpoints following the procedure described above.
Usage of a custom token format.
~~The token is not scope specific - it contains all scope available in~~ ~~B2ACCESS. Thus, by using it on one service, it reveals all access rights~~ ~~of the user on any service to the service provider, and it entitles the~~ ~~service provider to use any other of these services on behalf of the~~ ~~user.~~ The current solution allows the end-user to choose the scope from a drop-down menu.
The temporal limitation of the validity applies to all permissions equally.

As a result, in an environment where b2access is intended to manage EPOS autorisation to different types of services, the security level for all is defined by the weakest / least demanding participant.

This document describes a token based AAI mechanism within EIDA relying on current AAI standards and state-of-the-art concepts. In favor of a full featured token based AAI mechanism we partly must break compatibility with the current FDSN Web-Service standard for restricted data access.

Requirements

The new EIDA AAI has to meet the following requirements:

[X] A unique interface for protected resources of both EIDA gateway (e.g. federator) and endpoint services.
[X] Decoupling of AAI from resource servers; authorization is provided by means of an authorization server.
[X] Scriptability of access to resource servers.
[X] Scalability; compatibility with further services built on top e.g. EIDA Mediator or chained EIDA Federator instances
[X] Scalability in purpose; authentication/authorization information is specific to scope and does not unveil any available scope to any RS
[X] The usage of a well documented, ideally standardized structured token format. The token format should allow both digital signatures and digital encryption.
[X] No storage of access credentials/tokens at ERS/RS (between single requests). Stateless services.
[X] Reasonable access token lifetimes e.g. 3600s, however without inflicting restrictions on long-running data requests
[X] Simplicity: Transparent scope usage from the end user’s perspective. The scope must be validated by the API (i.e. protected resource) meanwhile the general authorization must be granted by the authorization server (example: the authorization server authorizes a user to request data of the scope “alparray”, but the RS checks which of the data requested by a user authorized for alparray actually belongs to this scope)
[X] Ability to add local user accounts to a federated identity provider.
[X] Ability to transparently revoke end user access permissions.
[X] Fully compatible with present standards.

Terminology

EIDA-ERS (EIDA Endpoint Resource Server) Endpoint resource server within EIDA providing protected resources. In case of EIDA endpoint resource servers implement the FDSN webservice interface. An exemplary implementation is the SeisComp3 FDSNWS implementation.

EIDA-GRS (EIDA Gateway Resource Server) Gateway resource server implementing protected resources within EIDA. Gateway resource servers build on top of either EIDA-ERS or other (chained) gateway resource servers, respectively. Within EIDA, gateway resource servers implement transparent facades. While in terms of the well-known Composite Design Pattern EIDA-ERS implementations correspond to the leafs, EIDA-GRS represent the composites.

EIDA-RS (EIDA Resource Server) Umbrella term of EIDA-ERS and EIDA-GRS. In terms of the Composite Design Pattern EIDA-RS correspond to components.

B2ACCESS (EUDAT Authorization Server) B2ACCESS is the name of the EUDAT authorization server. B2ACCESS implements an authorization and authentication infrastructure providing identity federation. This draft relies on the OAuth2.0/OIDC authorization server implementation of B2ACCESS. The expressions B2ACCESS and EUDAT-AS are used synonymously within this document.

EIDA-AS (EIDA Authorization Server) Authorization server built on top of B2ACCESS in order to fulfil EIDA AAI specific requirements.

B2ACCESS Constraints

As of 2019-01-14 the B2ACCESS OAuth2.0/OIDC implementation exclusively uses Bearer tokens (JWT may be implemented in future releases). The authentication grant types implemented are:

Authentication Code
Implicit.

Besides, refresh tokens may be used by clients.

A webhook (i.e. user defined HTTP callbacks triggered by events) based messaging system is not planned to be implemented. The current OAuth2.0/OIDC configuration can be found at https://b2access.eudat.eu/oauth2/.well-known/openid-configuration.

A major constraint is the lack of the <a href=”Resource Owner Password Credentials”>https://tools.ietf.org/html/rfc6749#section-1.3.3 grant type which would allow a trusted highly privileged application (i.e. EIDA-GRS instance) obtaining an access token.

There is no automatic interface to register (or renew the registration of) trusted applications.

EIDA AAI Overview

The following proposal is based on the well established OAuth2.0 standard (RFC6749 and RFC6750) as well as the constraints set by the EUDAT B2ACCESS authentication and authorization platform.

Basic Concepts:

Protected resources within EIDA implement a uniform OAuth2.0 bearer access token based API.
Access token instrospection / validation is performed by the EIDA authorization server (EIDA-AS).
EIDA-AS implements a context dependent access token cache allowing the secure storage of access tokens during protected requests sessions within EIDA.
Conceptually, the EIDA-AS extends a time-limited EUDAT access token request specifically to the processing time of the request at an EIDA-GRS, while autorization is still checked in real-time by EIDA-ERS

Token Based Authentication

For restricted data access all protected resources within EIDA MUST implement a stateless OAuth2.0 bearer access token based authentication interface. Authenticated requests MUST be performed using the Authorization request header field defined in Section 2.1 of RFC6750.

Protected resources from both EIDA-GRS and EIDA-ERS perform the access token validation using the EIDA Authorization Service (EIDA-AS). Thus, the access token is sent to the token endpoint as defined by section <a href=”Access Token Introspection”>Access Token Introspection. All protected resources of EIDA resource servers MUST perform this valdidation in order to be able to return the appropriate HTTP status codes in case of errors.

Once a protected resource of a EIDA-GRS receives a request containing a bearer access token, the EIDA-GRS MUST forward this access token for subsequent requests to EIDA-ERS. EIDA resource servers MUST NOT store access tokens between two single requests.

Protected Resource Request

Protected resources of EIDA-RS will implement authentication requests using the authorization request header field as defined in Section 2.1 of RFC6750. RFC6750 requires the usage of Transport Layer Security (TLS).

Request parameters for protected resources are equal to those for unprotected resources. Request parameters are defined in the FDSN Web-Service Specifications (Version 1.1b).

Besides, one additional parameter is introduced:

requestsessionids A string containing a comma-separated list of request session identifiers associated with the access token passed. The parameter MUST exclusively be set by EIDA-GRS. The parameter MUST be consumed by protected resource implementations within EIDA.

The following is a non-normative exemplary end-user client request:

GET /resource?net=Z3sta=A051&cha=HHZ HTTP/1.1
Host: server.example.com
Authorization: Bearer mF_9.B5f-4.1JqM

An exemplary non-normative EIDA internal request is:

POST /resource HTTP/1.1
Host: server.example.com
Accept: application/vnd.fdsn.mseed
Content-Type: application/x-www-form-urlencoded
Authorization: Bearer mF_9.B5f-4.1JqM

requestsessionids=05d940fdd4c279b47ab3e3b483e276a95cac [...]
Z3 A051 * * 2019-01-01T00:00:00 2019-02-01T00:00:00

The meaning of the requestsessionids parameter is explained in greater detail in section EIDA Authorization Service.

Protected resources of EIDA-GRS MUST only perform HTTP POST requests (RFC7231) to other protected resources within EIDA.

Protected Resource Response

If the access token validation (authentication) was successful and the client is authorized to request the data as specified the protected resource MUST return the data as defined in the FDSN Web-Service Specifications.

Error Codes

In case a request for restricted data fails, protected resources of EIDA-RS MUST return HTTP status codes as defined in the FDSN Web-Service Specifications.

invalid_request In addition to the reasons defined in the FDSNWS specifications the EIDA resource server MUST return HTTP 400 (Bad Request) status code if a method including an access token is different as defined above.

invalid_token The access token provided is expired, revoked, malformed, or invalid for other reasons. The EIDA-RS MUST respond with the HTTP 401 (Unauthorized) status code. The client MAY request a new access token from B2ACCESS and retry the protected resource request.

insufficient_scope An EIDA resource server MUST return HTTP 403 (Forbidden) status code if the request requires higher privileges than provided.

If the request lacks any authentication information (e.g. the client was unaware that authentication is necessary or attempted using an unsupported authentication method), the resource server MUST NOT include an error code or other error information.

EIDA Authorization Service

Access tokens may expire during protected EIDA-GRS request sessions. For this reason EIDA-AS is implemented. The service implements a centralized context dependent cache virtually extending the lifetime of access tokens for request sessions within EIDA. EIDA-AS is implemented as a adapting wrapper of B2ACCESS.

Communication between protected resources and EIDA-AS MUST be protected with a secure HTTP connection such as SSL/TLS (RFC2818).

Context Dependent Access Token Cache

EIDA-AAI uses plain bearer access tokens in order to authenticate clients. Due to security reasons, such access tokens usually expire within minutes. However, since a single request to a protected resource of a EIDA-GRS may lead to multiple requests to other protected resources within EIDA (demultiplexing) the access token may expire during this session. In order to hide the access token expiration and its consequences from the end-user, EIDA-AAI must introduce the concept of a secure access token cache implementing the secure temporary storage of access tokens due to EIDA-GRS request sessions.

EIDA-GRS are implemented as transparent facades i.e. a client also is allowed to use EIDA-ERS directly. To increase usability both unprotected and protected resources within EIDA SHOULD implement a uniform API. Until now, EIDA has no standardized mechanism to distinguish a direct end-user request from an internal request.

In order to allow protected resources to distinguish between a direct end-user request to a protected resource and an internal protected request session within EIDA (i.e. a protected request from a EIDA-GRS) we introduce the concept of a EIDA-GRS request session identifier access token context.

Protected resources of EIDA-GRS must keep track of request session identifiers in order to reference the access token with EIDA-AS.

A context dependent access token cache is implemented by the EIDA-AS. In the context of protected resources within EIDA, EIDA-AS adapts the interface of B2ACCESS. This approach has two main advantages:

Authorization server singleton: There is only one single authorization service, namely EIDA-AS.
Maintainability: While the interface of the third-party service B2ACCESS may change over time the interface of EIDA-AS may remain unchanged.

Protocol Flow

A client may access protected resources within EIDA either by means of an EIDA-GRS (i.e. proxied access) or an EIDA-ERS (i.e. direct access).

Direct Access To Protected EIDA Endpoint Resources

Directly accessing a protected resource of a EIDA-ERS implies that no access token previously was cached with EIDA-AS. If a client requests data from a EIDA-ERS directly, the protected resource firstly MUST introspect the access token with EIDA-AS. Introspection endpoint requests MUST be performed as defined below.

For a valid request to the access token introspection endpoint of EIDA-AS, the authorisation server will respond with a JSON object (RFC7159) with the active field set to true and an optional scope field. If the response contains a scope field and the protected resource is implemented by an EIDA-ERS, the protected resource MUST perform a scope related validation. If successful, the client’s call to the protected resource endpoint MUST respond in accordance with the FDSNWS specifications.

Proxied Access To Protected EIDA Endpoint Resources

A. A client calls a protected resource implemented by a EIDA-GRS as defined in Section Protected Resource Requests.

B. The protected resource registers the bearer access token passed with the token registration endpoint of the authorization server i.e. EIDA-AS. If EIDA-AS was not able to successfully register a protected request session the protected resource returns a response as defined in Section <a href=”Protected Resource Response And Error Response”>Protected Resource Response And Error Response. If the protected request session was successfully initialized EIDA-AS returns a <a href=”Request Session Identifiers”>request session identifier.

C. The protected resource implemented by EIDA-GRS calls protected resources of EIDA-ERS instances necessary to fullfil the client’s request. The EIDA-ERS protected resource calls now ship the request_session_ids parameter with the value returned from the registration endpoint of EIDA-AS.

D. Once a protected resource implemented by a EIDA-ERS receives the request, firstly, the bearer access token is validated with the token introspection endpoint of EIDA-AS. The request is performed as defined in section <a href=”Token Introspection Request”>Token Introspection Request. Now, the received request session identifier is included with the token introspection request. Next, the protected resource MUST verify if the client was authorized considering the token’s scope. Only, if both the token introspection and the scope validation was successful the protected resource MUST return data.

E. D is repeated until all GRS->ERS requests relating to one client->GRS request are completed.

F. If the protected resource of the EIDA-GRS received all data neccessary to fulfil the clients request, the protected resource MUST unregister the protected resource session previously registered. For this purpose, the protected resource calls the token unregistration endpoint of EIDA-AS as defined in Section Unregistration Request.

Chaining Protected Resource Servers

When chaining several EIDA-GRSs an access token may expire on his way from one EIDA-GRS_i to the next EIDA-GRS_i+1. If EIDA-GRS_i+i now wants to register the access token with EIDA-AS, EIDA-AS would not be able to validate the access token with B2ACCESS, anymore. However, in the context of the cached access token from EIDA-GRS_i the access token registration of EIDA-GRS_i+1 still should be valid.

The problem is solved with chained request session identifiers. Thus, both internal protected resource requests and requests for access token registration with EIDA-AS must contain at least one request identifier.

Request Session Identifiers

Request session identifiers are critial in the context of security.

Request session identifiers MUST be implemented as hexadecimal encoded opaque tokens.

A request session identifier opaque token MUST have a minimum length of 255 bytes.

The usage of request session identifiers requires protected resources of EIDA-GRS to implement a bookkeeping mechanism for protected request sessions. The implementation of such a mechanism is out of scope of this document.

Access Token Registration

Within EIDA exclusively EIDA-GRSs MUST register access tokens with the EIDA-AS cache. For an EIDA-GRS the process of access token registration is equal to access token validation. No further access token introspection should be performed.

Registration Request

Note: Access token registration exclusively SHOULD be granted to previously registered EIDA-GRSs. Both implementation and level of protecting the access still needs to be discussed.

The protected resource calls the access token registration endpoint using an HTTPS POST RFC7231 request with parameters sent as application/x-www-form-urlencoded data as defined in W3C.REC-html5. The request defines the following parameters:

access_token REQUIRED. The bearer access token as used by B2ACCESS.

request_session_ids (request session identifiers) OPTIONAL. A comma-separated string of unique request session identifiers mapping the access token in the EIDA-AS cache. If no request session identifier is present or the parameter is not passed, EIDA-AS assumes that a new request session must be initialized. Hence, EIDA-AS firstly verifies the access token with B2ACCESS. If the access token validation was successful, the access token is cached. For one or more request session identifiers, EIDA-AS assumes that the access token is used in a chained EIDA-GRS environment. EIDA-AS does not verify the access token with B2ACCESS anymore - but does verify the access token with previously cached access tokens.

cache_invocation (cache invocation) The cache invocation claim identifies the access token’s cache expiration time on or after the AT MUST NOT be cached anymore. The processing of the cache invocation claim requires that the current date/time MUST be before the expiration date/time listed in the cache invocation claim. Its value MUST be a number NumericDate value. If the cache invocation time expired EIDA-AS MUST invalidate the access token request session. The implementation of this claim is OPTIONAL.

In future, the access token registration endpoint MAY accept additional parameters to provide further context to the access token caching session. For instance, an aud (audience) parameter could be defined restricting the protected resources the access token caching session is intended for. An exemplary implementation of such a parameter is described in Section 4.1.3 of RFC7519.

Registration Response

For an EIDA-GRS access token registration with EIDA-AS follows the principle access token registration means access token validation. Hence, the registration endpoint response corresponds to the <a href=”Token Introspection Response”>introspection endpoint response.

For a successful access token registration EIDA-AS additionally MUST include the following top-level response member:

request_session_id REQUIRED. JSON string of a request session identifier referencing the access token within the EIDA-AS cache. In a chained EIDA-GRS environment the protected resource SHOULD append this identifier to the list of received request session identifiers and include it with subsequent requests.

Error Response

The registration endpoint error response corresponds to the introspection endpoint error response.

Access Token Introspection

In order to provide access token introspection EIDA-AS implements the introspection endpoint. Note, that the token introspection has not to be confused with the token validation endpoint implemented by B2ACCESS.

Token Introspection Request

Note: RFC7662 specifies the introspection endpoint to be protected. How the protection of the resource should look like (e.g. format, standard, etc.) is still to be discussed.

Protected resources within EIDA MUST perform the token introspection request as defined in RFC7662.

If the protected resource received a single or multiple request identifiers from a client, the request identifier MUST be used unchanged when performing a request to the access token introspection endpoint. Request identifiers are included as follows:

request_session_ids String containing a comma-separated list of request session identifiers associated with the access token in the cache. Sequence does not matter.

Token Introspection Response

The EIDA-AS token introspection endpoint responds with a JSON object in application/json format with the following top-level members:

active REQUIRED. Boolean indicator of whether or not the presented token is currently active. A true indicates that the given token is either cached or not expired.

scope OPTIONAL. A JSON string containing a space-separated list of scopes associated with this token, in the format described in Section 3.3 of OAuth 2.0 (RFC6749).

sub OPTIONAL. Subject of the token, as defined in JWT (RFC7519). Usually a machine-readable identifier of the resource owner who authorized this token.

To prevent EIDA resource servers from any ambiguities the token introspection endpoint response MUST NOT contain the exp claim as defined in (RFC7519).

If the introspection call is properly authorized but the token is not active, does not exist on this server (or the protected resource is not allowed to introspect this particular token), then the authorization server MUST return an introspection response with the active field set to false.

The following is a non-normative example response:

HTTP/1.1 200 OK
Content-Type: application/json

{
  "active": false
}

To avoid disclosing the internal state of the authorization server, the introspection response for an inactive token MUST NOT contain any additional claims beyond the required active claim (with its value set to false).

Error Response

On errors EIDA-AS implements the behaviour as defined in Section 2.3 of RFC7662.

Access Token Unregistration

EIDA-AS MUST guarantee that access token unregistration is exclusively performed by the protected resource of the EIDA-GRS which previously registered the access token. Note, that this requires identifying protected resources within EIDA uniquely. The implementation of such a unique identification mechanism still needs to be discussed.

Unregistration Request

The protected resource calls the access token unregistration endpoint using an HTTP DELETE (RFC7231) request with parameters sent as application/x-www-form-urlencoded data as defined in W3C.REC-html5. The following parameters are sent:

access_token REQUIRED. String containing a single access token to be removed.

request_session_ids REQUIRED. String containing a space-separated list of unique request session identifiers associated with the access token. If multiple request session identifiers are sent EIDA-AS invalidates the access token cached with the context of the last request session identifier in the list.

Unregistration Response

The authorization server responds with a JSON object (RFC7159) in application/json format with the following top-level members:

token The access token removed from the authorization server cache.

The following is a non-normative example response:

HTTP/1.1 200 OK
Content-Type: application/json

{
  "token": "2YotnFZFEjr1zCsicMWpAA"  
}

Error Response

If the protected resource requesting access token unregistration is not authorized to execute its call to the unregistration endpoint, the authorization server will respond with HTTP 401 (Unauthorized).

If the protected resource authenticated successfully and the request was not well formatted or there is a mismatch between the parameters and values sent, the access token unregistration endpoint will respond with an HTTP 400 (Bad Request).

Token Revocation

Due to the fact, that a protected request session may exceed the access token expiration time, EIDA-AS SHOULD implement a token revocation endpoint. If a client calls this endpoint EIDA-AS MUST guarantee that the revocation request is propagated to B2ACCESS.

TODO: Implementation details of the revocation endpoint. Note, that OAuth2.0 Token Revocation (RFC7009) defines a revocation endpoint implementation.

EIDA Protected Resource Registration

This section still is has to be discussed. See also the section with <a href=”Open Questions”>open questions.

Assuming protected resources authentication is based on certificates, EIDA-AS MAY accept all protected resources certified by a trusted CA. Restriction of protected resources due to the IP address range utilized may be implemented, optionally.

EIDA-AS And B2ACCESS Synchronization

The registration of an access token request session with EIDA-AS MUST be only valid if EIDA-AS was able to successfully cache token related data from the B2ACCESS token information endpoint. Optionally, EIDA-AS will try to fetch data from the B2ACCESS user information endpoint.

EIDA-AS will temporarily cache this data. EIDA-AS MUST remove the data as soon as the protected resource asks EIDA-AS to unregister the access token’s request session.

It is on the client’s own responsibility to negotiate with B2ACCESS the correct attributes and scope the access token is issued for. // does B2ACCESS allow for token requests with selective scope?

Internally, EIDA-AS SHOULD periodically synchronize with B2ACCESS the state of the access tokens cached. Depending on the refresh rate and the access token’s expiration time EIDA-AS is able to detect revoked tokens, too. If a protected request session exceeds the access token’s expiration time synchronization with B2ACCESS is not possible, anymore. For the purpose of revocation EIDA-AS SHOULD implement its own token revocation endpoint. Token revocation requests and responses are not specified, yet.

EIDA-AS B2ACCESS Adapter

For protected resources of EIDA-RS solely EIDA-AS is used as authorization server. EIDA-AS adapts the access token validation related interface of B2ACCESS for EIDA internal purposes.

For the purpose of e.g.

implementation of OAuth2.0 authorization grant types
obtaining an access token
making use of refresh tokens

clients preliminary should stick to the API provided by B2ACCESS.

Design Considerations

Advantages & drawbacks of this architecture are:

All protected resource implementations support a unique interface for the sake of scalability. Also, a scenario with multiple chained EIDA-GRS may be feasible. While the scope management and user provisioning is implemented by B2ACCESS the scope is evaluated and validated from EIDA-RS instances. In addition, users easily may be revoked. That is possible even during a request processed by an EIDA-GRS.
The design proposed tries to keep it simple i.e. protected resources of EIDA-GRS exclusively register protected request sessions meanwhile protected resources of EIDA-ERS perform only access token introspection.
Protected resources within EIDA do not need to change their behaviour depending on request session identifiers. Request session identifiers are simply passed to EIDA-AS. Decision making is encapsulated within EIDA-AS.
When registering a protected request session with EIDA-AS, the protected resource of the EIDA-GRS should append the identifier to the request session identifiers received.
This approach may enable EIDA-AS to order request session identifiers hierarchically.

In particular, this design may be useful in a chained EIDA-GRS environment.
Token introspection is tightly coupled to EIDA-AS / B2ACCESS. If EIDA grows this probably will result in an increasingly chatty system bound to those authorization servers. In future, this issue might be solved using self containing descriptive tokens e.g. JWT (RFC7519). However, as long as B2ACCESS OAuth2.0 is based on plain bearer access tokens only, EIDA-AS should implement the same facilities.
In theory, all protected resources of EIDA-RS implementations may both register and introspect access tokens with EIDA-AS. At the time being, there is no mechanism implemented enforcing that exclusively protected resources of EIDA-GRS are allowed to register/unregister protected request sessions with EIDA-AS, and reversely, that protected resources implemented by EIDA-ERS are restricted to exclusively perform token introspection. I.e. it is only this document enforcing this restriction.
Implementing a different behaviour would break with the proposed EIDA-AAI architecture.

Note, that enforcing the restriction would require to distinguish between EIDA-GRS instances and EIDA-ERS instances. In future, this distinction may be implemented by e.g. an EIDA (protected) resource registry.
Restricting access token sessions to a subset of the protected resources within EIDA would introduce an additional mechanism to increase security. Only those protected resources would be allowed to introspect the access token session previously determined by the EIDA-GRS registering the access token session.
Again, enforcing requires the implementation of an EIDA (protected) resource registry unambigously identifying protected resources within EIDA.
The design is both flexible and sustainable. The implementation of EIDA-AS is exclusively required to allow protected resources implemented by EIDA-GRS instances request processing durations greater than access token lifetimes. As a consequence, EIDA-AS would become obsolete if B2ACCESS (or any other authorization server implementing the OAuth2.0 specification) would enable the OAuth2.0 Resource Owner Password Credentials Grant Type. Hence, EIDA-GRS instances could be considered as highly trusted clients within EIDA and would be allowed to obtain an access token from the OAuth2.0 authorization server (after a successful authentication) in case the access token’s lifetime exceeded.
Removing EIDA-AS would have the following (minor) consequences:
- Protected resources of EIDA-GRS implementations would need to adjust their protocol flow.
- Protected resources of EIDA-ERS would need to validate/introspect the access token with the OAuth2.0 authorization server instead with EIDA-AS.
- The requestsessionid query parameter would become obsolete and could be removed.
However, from the end-user’s point of view the API of protected resources within EIDA would remain unchanged.

Refresh Tokens

Clients MAY make use of refresh tokens as defined in Section 1.5 of OAuth2.0 (RFC6749). Refresh tokens allow to replace an expiring token by using the previous one, rather than a human user interaction, for authentication.

In order to obtain a new access token using refresh token credentials, a client should directly negotiate with B2ACCESS. Further details are given in the B2ACCESS instruction manual.

EIDA Scope Management

Scopes SHOULD be unique within EIDA. Besides, scopes should be consistent between protected resources of EIDA-RS and B2ACCESS.

The scope syntax MUST respect the requirements defined in Section 3.3 of OAuth2.0 (RFC6749). URI namespace identifiers SHOULD be used.

A more detailed description on how to manage scopes requires coordination within EIDA (and EPOS) but is beyond the scope of this purposal.

Open Questions

[X] Should protected resources of EIDA-RS implement both HTTP POST and GET methods? If clients make use of the HTTP GET method it should be taken into consideration that access tokens might be logged.
The question somehow messes up RFC6750’s description of authenticated requests to protected resources of EIDA-RS. According to RFC6750 (section 2.1) protected resources within EIDA MUST implement authentication for HTTP GET requests using the Authorization request header field. Besides, protected resources MUST implement authenticated access by means of the HTTP POST method RFC6750 section 2.2. Authenticated access using the HTTP GET method including the access token as a URI query parameter MUST NOT be implemented.
[ ] For the purpose of access token session registration/unregistration EIDA-AS needs to uniquely identify protected resources of EIDA-GRS ideally independent from the resource server’s IP address. Which approach to be chosen to implement unique identification?
Suggestion: Protected resource certificate authentication:

EIDA-AS authenticates protected resources of EIDA-RS by means of certificates and optionally by checking the IP address range. Calls from protected resources to the registration, introspection and unregistration endpoint of EIDA-AS may be signed. Signing might be implemented by e.g.:
- HTTP Signatures (Draft) (marked as work in progress). An exemplary implementation is provided by e.g. requests-http-signature.
- Payload signature by means of JWT (RFC7519)
- Custom payload signature as proposed by Andres H. (PGP ASCII-armored clearsigned)
HTTP Signatures (Draft) and the custom PGP based payload signature would be compatible with standards such as RFC7662 (Oauth 2.0 token introspection).

JWT (RFC7519) both is well standardized and provides payload signature JWS (RFC7515), however, its usage is not compatible with OAuth2.0 Token Introspection (RFC7662).
[ ] As a consequence of the previous question and the purposed solution, a second question arises: Which approach to be chosen in order to obtain an automatic certificate signing request (CSR) infrastructure?
Suggestions:

Ideally, EIDA-AS implements its own custom CSR endpoint. Hence, public keys of protected resources would be signed by a EIDA online certificate authority (CA). The largest benefit: Access control to EIDA-AS depends exclusively on the EIDA online CA. Even though this approach seems to be the most generic, further questions arise, such as:
- Costs of implementing own CSR infrastructure?
- Which approach to be chosen in order to obtain automatic CSR issued? (An exemplary approach may be Let’s Encrypt’s certbot).
- …
B2ACCESS implements a CSR endpoint. Certificates are issued based on the online EUDAT CA. In principle, protected resources may use this facility to obtain certificates. Limitations and restrictions are:
- Certificates have a lifetime limited to 12 hours. As a consequence, protected resources of EIDA-RS instances would need to repeatedly issue CSRs (e.g. every 9 hours). Furthermore, installing and renewing the certificates manually is not an option.
- In order to issue a CSR, protected resources within EIDA would need to be equipped with a CSR issuing tool similar to Let’s Encrypt’s certbot. This EIDA CSR-tool (EIDA-CSR) would need to be A) registered as B2ACCESS OAuth2.0 client (Currently, registration of trusted clients seems to be possible only manually.) B) implement one of the OAuth2.0 flows allowed by B2ACCESS.
- Besides, a technical user would be required to obtain OAuth2.0 bearer access tokens from B2ACCESS.
Alternatively, another third-party CA may be used.

Pros:
- Security
- Scalability; includes automatic protected resource provisioning
- The CA decouples protected resources from authorization server (i.e. EIDA-AS)
- Certificate based authentication makes further protection of EIDA-AS resources obsolete (e.g. password based authentication etc).
Cons:
- Additional complexity

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EIDA AAI based on B2ACCESS OAuth2.0 (Draft)

Introduction

Requirements

Terminology

B2ACCESS Constraints

EIDA AAI Overview

Token Based Authentication

Protected Resource Request

Protected Resource Response

Error Codes

EIDA Authorization Service

Context Dependent Access Token Cache

Protocol Flow

Direct Access To Protected EIDA Endpoint Resources

Proxied Access To Protected EIDA Endpoint Resources

Chaining Protected Resource Servers

Request Session Identifiers

Access Token Registration

Registration Request

Registration Response

Error Response

Access Token Introspection

Token Introspection Request

Token Introspection Response

Error Response

Access Token Unregistration

Unregistration Request

Unregistration Response

Error Response

Token Revocation

EIDA Protected Resource Registration

EIDA-AS And B2ACCESS Synchronization

EIDA-AS B2ACCESS Adapter

Design Considerations

Refresh Tokens

EIDA Scope Management

Open Questions

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