rfc-compliance

name	rfc-compliance
description	Verify OAuth protocol implementations stay aligned with relevant RFCs. Use when adding or modifying grant flows, token responses, error formats, redirect behavior, introspection, revocation, PKCE, or metadata endpoints in Doorkeeper.

RFC Compliance

When implementing or modifying OAuth protocol behavior in Doorkeeper, use this skill to verify the implementation stays aligned with the relevant RFCs.

Core RFCs

RFC	Topic	Key Files
6749	OAuth 2.0 Framework	lib/doorkeeper/oauth/, app/controllers/doorkeeper/
6750	Bearer Token Usage	lib/doorkeeper/oauth/token.rb, lib/doorkeeper/rails/helpers.rb
7009	Token Revocation	app/controllers/doorkeeper/tokens_controller.rb (revoke action)
7636	PKCE	lib/doorkeeper/oauth/pre_authorization.rb, lib/doorkeeper/oauth/authorization_code_request.rb
7662	Token Introspection	lib/doorkeeper/oauth/token_introspection.rb
8252	OAuth for Native Apps	lib/doorkeeper/oauth/helpers/uri_checker.rb (loopback)
9207	Authorization Server Issuer Identification	lib/doorkeeper/oauth/code_response.rb (iss param)
8707	Resource Indicators	lib/doorkeeper/oauth/resource_indicator_validator.rb

Error Response Format (RFC 6749 §5.2)

Token endpoint errors MUST include:

• error — single ASCII error code (required)
• error_description — human-readable description (optional)
• HTTP status codes: 400 for most errors, 401 for invalid client auth

Valid error codes for the token endpoint: invalid_request, invalid_client, invalid_grant, unauthorized_client, unsupported_grant_type, invalid_scope

Reference: lib/doorkeeper/oauth/error_response.rb

Authorization endpoint errors that are redirectable include error, error_description, and state in the redirect. Non-redirectable errors (invalid redirect_uri, invalid client_id) MUST NOT redirect — render an error page instead.

Reference: lib/doorkeeper/oauth/pre_authorization.rb — redirectable? logic

Token Response Format (RFC 6749 §5.1)

Successful token responses MUST include:

• access_token — the token value
• token_type — "Bearer" (case-insensitive per RFC 6750)
• expires_in — lifetime in seconds (recommended)

MAY include:

• refresh_token
• scope — if different from requested

MUST NOT include:

• refresh_token in implicit grant responses

Reference: lib/doorkeeper/oauth/token_response.rb

Authorization Code Flow (RFC 6749 §4.1)

1. Authorization request → PreAuthorization validates, Code issues grant
2. Token request → AuthorizationCodeRequest validates grant + issues token

Key constraints:

• Code is single-use (§4.1.2) — revoke tokens on replay
• Code must be bound to client_id and redirect_uri
• Code SHOULD expire in max 10 minutes (configurable via authorization_code_expires_in)
• redirect_uri in token request must match the one used in authorization request

PKCE (RFC 7636)

• code_challenge_method defaults to "plain" when omitted (§4.2) — but Doorkeeper intentionally requires it when code_challenge is present (secure-by-default deviation)
• S256: BASE64URL(SHA256(code_verifier)) must equal code_challenge
• plain: code_verifier must equal code_challenge
• code_verifier is 43-128 characters from [A-Z] / [a-z] / [0-9] / "-" / "." / "_" / "~"

Token Introspection (RFC 7662)

• MUST require authentication of the requesting party
• Response for inactive/invalid tokens: {"active": false} — no other fields
• Response for active tokens includes: active, scope, client_id, token_type, exp, iat, sub, aud, iss
• Doorkeeper omits token_type and exp for refresh tokens in introspection responses (these fields are OPTIONAL per §2.2, not prohibited — but they are semantically inapplicable to refresh tokens)

Reference: lib/doorkeeper/oauth/token_introspection.rb

Token Revocation (RFC 7009)

• Return 200 OK even for invalid/unknown tokens (§2.1) — prevents token enumeration
• Client authentication is required
• The token_type_hint parameter is optional; server must still check both types
• Revoking an access token SHOULD revoke associated refresh token (and vice versa)

Current known deviation: Doorkeeper returns 403 when the token belongs to a different client, rather than 200.

Bearer Token Errors (RFC 6750 §3)

• 401 responses MUST include WWW-Authenticate: Bearer header
• Error codes in WWW-Authenticate: invalid_request, invalid_token, insufficient_scope
• 403 for insufficient_scope, 401 for invalid_token, 400 for invalid_request

Reference: lib/doorkeeper/oauth/error_response.rb — authenticate_info method

Resource Indicators (RFC 8707)

• Resource URIs must be absolute and must not contain a fragment
• Multiple resources use repeated resource parameters (Rack limitation: use resource[] syntax)
• Tokens are audience-restricted to the declared resources
• Refresh requests enforce subset restriction against original grant

Reference: lib/doorkeeper/oauth/resource_indicator_validator.rb

Authorization Server Metadata (RFC 8414)

Served at /.well-known/oauth-authorization-server. Must include:

• issuer — MUST be identical to the iss in authorization responses
• authorization_endpoint, token_endpoint
• response_types_supported, grant_types_supported
• token_endpoint_auth_methods_supported
• scopes_supported (recommended)

Reference: lib/doorkeeper/oauth/metadata_response.rb

Implementation Patterns

Adding a new grant type

1. Create a strategy class in lib/doorkeeper/request/ extending Doorkeeper::Request::Strategy
2. Create a request class in lib/doorkeeper/oauth/ extending Doorkeeper::OAuth::BaseRequest
3. Register with Doorkeeper::GrantFlow.register in lib/doorkeeper/grant_flow.rb
4. Add to default grant_flows if it's a standard flow
5. Add specs in spec/requests/flows/ and spec/lib/oauth/

Adding a new error code

1. Add to lib/doorkeeper/errors.rb as a new class inheriting BaseResponseError
2. Add I18n key in config/locales/en.yml
3. Map to correct HTTP status in the error class's #type method

Adding a new configuration option

1. Add via option DSL in lib/doorkeeper/config.rb
2. Add validation in lib/doorkeeper/config/validations.rb if needed
3. Document in the initializer template: lib/generators/doorkeeper/templates/initializer.rb
4. Add specs in spec/lib/config_spec.rb

Verification

After implementing protocol changes:

1. Run flow specs: bundle exec rspec spec/requests/flows/
2. Run endpoint specs: bundle exec rspec spec/requests/endpoints/
3. Run OAuth unit specs: bundle exec rspec spec/lib/oauth/
4. Verify metadata response: bundle exec rspec spec/requests/endpoints/metadata_spec.rb