docs: updates documents regarding Agents As Principals (Limited EA) [EUP-870]

[silviom]

Description

Documents the client-observable Authentication API surface of Agents as Principals on the existing API reference pages. The feature makes an AI agent a first-class OAuth principal: when a tenant has the feature enabled and a resource server opts in with agent_subject_claims: 'auth0-v1', access tokens issued for agent-linked applications carry new identity claims and an adjusted sub.

Incidental fix:
The sample discovery document was missing a comma after "PS256" in token_endpoint_auth_signing_alg_values_supported, making the snippet invalid JSON. Fixed while editing the same block.

References

https://auth0team.atlassian.net/browse/EUP-870

Testing

1. cd main && mint dev, then review the changed pages:
   • /docs/api/authentication/client-credential-flow/get-token
   • /docs/api/authentication/authorization-code-flow/get-token
   • /docs/api/authentication/on-behalf-of-token-exchange/get-token
   • /docs/api/authentication/custom-token-exchange/get-token
   • /docs/get-started/applications/configure-applications-with-oidc-discovery
   • /docs/secure/call-apis-on-users-behalf/on-behalf-of-token-exchange
   • /docs/secure/tokens/access-tokens/access-token-profiles
2. cd main && mint broken-links — the new cross-links to
   /docs/ai-agents-mcp/agents-as-principal/agent-identity-in-tokens,
   /docs/secure/tokens/access-tokens/access-token-profiles#claims, and
   /docs/secure/call-apis-on-users-behalf/on-behalf-of-token-exchange#the-act-claim must resolve.
3. Confirm the discovery snippet parses as JSON after the comma fix.
4. Claim-by-claim verification against auth0-server is recorded in the EUP-870 Authentication API external
   contract (master 9fedcd85df); the delegation-depth behaviour is covered by
   on_behalf_of_token_exchange_exchange_flow.actor.tests.js and
   AccessTokenTypeSubjectTokenParser.test.js.

Checklist

• I've read and followed CONTRIBUTING.md.
• I've tested the site build for this change locally.
• I've made appropriate docs updates for any code or config changes.
• I've coordinated with the Product Docs and/or Docs Management team about non-trivial changes.

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Summary

Status	Count
🔍 Total	70
✅ Successful	26
⏳ Timeouts	0
🔀 Redirected	3
👻 Excluded	41
❓ Unknown	0
🚫 Errors	0
⛔ Unsupported	0

Redirects per input

Redirects in main/docs/api/authentication/custom-token-exchange/get-token.mdx

• [200] https://auth0.com/docs/customize/actions | Redirect: Followed 1 redirect resolving to the final status of: OK. Redirects: https://auth0.com/docs/customize/actions --> https://auth0.com/docs/customize/actions/actions-overview

Redirects in main/docs/get-started/applications/configure-applications-with-oidc-discovery.mdx

• [200] https://www.rfc-editor.org/rfc/rfc8414 | Redirect: Followed 1 redirect resolving to the final status of: OK. Redirects: https://www.rfc-editor.org/rfc/rfc8414 --> https://www.rfc-editor.org/info/rfc8414/

Redirects in main/docs/secure/call-apis-on-users-behalf/on-behalf-of-token-exchange.mdx

• [200] https://www.rfc-editor.org/rfc/rfc7638 | Redirect: Followed 1 redirect resolving to the final status of: OK. Redirects: https://www.rfc-editor.org/rfc/rfc7638 --> https://www.rfc-editor.org/info/rfc7638/
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