[Tr00d]

Summary

Admins can list the custom OAuth/OIDC providers registered on the project, optionally only those of one type.

Capability: auth.admin.list_providers: Admin List Providers.

Stacked on #591 (auth.admin.get_provider), which is stacked on #590 (auth.admin.create_provider). This PR's base is feat/auth.admin.get_provider, so the diff shows only the list capability. Retarget it once the PRs below it merge.

Public API

// IGotrueAdminClient<TUser>
Task<IReadOnlyList<CustomProvider>> ListCustomProvidersAsync(CustomProviderType? type = null, CancellationToken cancellationToken = default);

using Supabase.Gotrue.Common;

var admin = new AdminClient(serviceRoleKey, new ClientOptions { Url = authUrl });
var oidcProviders = await admin.ListCustomProvidersAsync(CustomProviderType.Oidc);

New types: none. It uses CustomProvider and CustomProviderType from #590. IGotrueApi<TUser, TSession> gains the matching ListCustomProvidersAsync(string jwt, CustomProviderType?, CancellationToken).

Behavior

Operation	GET /admin/custom-providers with the service-role key. Adds ?type=oauth2 or ?type=oidc when type is given; sends no query when it is null.
Input	type, optional. The enum makes the server's 400 for an invalid type impossible to reach.
Output	200 {"providers":[…]} → read-only list in server order. A null or absent providers, or a null body, gives an empty list.
Failures	GotrueException: Reason = AdminTokenRequired on 401/403; ErrorCode = feature_disabled on 404 when custom providers are disabled
State	None

Deviations from supabase-js

• An enum instead of the 'oauth2' | 'oidc' string union.
• Failures throw. supabase-js returns an empty list together with the error.

Tests

Tier	Class	Pins
E2E	ListCustomProvidersTests	A seeded OAuth2 provider is listed with no filter and with OAuth2, and left out with Oidc. Non-admin key → AdminTokenRequired.
Contract	ListCustomProvidersContractTests	Route and credentials, and no type query when unfiltered. type query for each enum value. Every listed provider mapped. Null, absent or missing providers → empty list. A cancelled token sends nothing. The call completes when the caller blocks on a context that never runs continuations.

Changed-line coverage: 100% (8 lines on top of #591). Mutation: 5/5 killed on changed lines, 0 survivors (3 compile errors, 1 ignored).

No wire-shape approval snapshot: the request has no body.

Layout

packages/Gotrue/Gotrue/ListCustomProviders/
  CustomProviderListResponse.cs   internal: the {"providers": [...]} wire DTO and its mapping
  ListCustomProvidersQuery.cs     internal: the ?type= filter
packages/Gotrue/Gotrue.Tests/ListCustomProviders/