[Server] OIDC discovery fails for issuers with a trailing slash #507

OIDC discovery fails for issuers with a trailing slash

OidcDiscovery::fetchMetadata() strips the trailing slash from the issuer before discovery:

$issuer = rtrim($issuer, '/');

The normalized issuer is then used to validate the issuer returned in the discovery metadata.

This causes discovery to fail for providers that use a trailing slash in their canonical issuer, such as Authentik:

Expected: https://auth.example.com/application/o/mcp
Got:      https://auth.example.com/application/o/mcp/

The trailing slash should only be removed when building the discovery URL. The original issuer should be preserved for validation.

Related PR