@spec register(
  String.t(),
  keyword()
) ::
  {:ok, %{client_id: String.t(), client_secret: String.t() | nil}}
  | {:error, term()}

Register a new OAuth client with the authorization server.

Uses RFC 7591 Dynamic Client Registration to automatically obtain a client_id without requiring manual pre-registration.

Parameters

• registration_endpoint: The registration endpoint URL from discovery
• opts: Optional overrides
  • :client_name - Application name (default: "fnord")
  • :redirect_uris - Callback URIs (default: ["http://127.0.0.1/callback"])

Returns

• {:ok, %{client_id: String.t(), client_secret: String.t() | nil}}

• {:error, reason}