feat(auth): add OAuth 2.1 authorization consent management API calls

[cemalkilic]

Summary

Adds user-facing OAuth authorization methods to @supabase/auth-js for building consent pages when Supabase Auth acts as an OAuth 2.1 authorization server.

Implements the consent flow where users approve/deny OAuth client authorization requests.

New API

Namespace: auth.oauth.*

Three new methods for managing OAuth authorization consent:

// Get authorization details (client info, scopes, user)
const { data, error } = await supabase.auth.oauth.getAuthorizationDetails(
  authorizationId,
  { skipBrowserRedirect?: boolean }
)

// Approve authorization request
const { data, error } = await supabase.auth.oauth.approveAuthorization(
  authorizationId,
  { skipBrowserRedirect?: boolean }
)

// Deny authorization request
const { data, error } = await supabase.auth.oauth.denyAuthorization(
  authorizationId,
  { skipBrowserRedirect?: boolean }
)

Use Case

Enables developers to build custom OAuth consent pages for their Supabase projects when acting as an OAuth 2.1 authorization server. Example flow:

1. User is redirected to consent page with authorization_id in URL
2. App calls getAuthorizationDetails(authorizationId) to fetch client and scope info
3. User reviews and clicks "Approve" or "Deny"
4. App calls approveAuthorization() or denyAuthorization()
5. SDK auto-redirects back to OAuth client with authorization code/error

What's NOT Included

Third-party OAuth client integration (calling /oauth/authorize and /oauth/token from external apps) is intentionally not included in this PR.

Rationale:

• Standard OAuth 2.1 client libraries already handle this well
• Would require full OAuth client lifecycle (refresh tokens, expiration, storage)
• Better served by documentation + existing OAuth libraries
• This PR focuses on the unique Supabase-specific consent management API, utilizing the existing Supabase session

Third-party integration will be addressed through comprehensive documentation showing how to use standard OAuth client libraries with Supabase Auth endpoints.

Breaking Changes

None. This is a purely additive change with zero breaking changes to existing APIs

[coveralls]

coverage: 95.455% (-0.5%) from 95.986%
when pulling 0d7a77a on cemal/feat-auth-add-oauth-endpoints
into c5ad2f4 on master.