Function handle_authorize 

pub fn handle_authorize(proxy: &OAuthProxyConfig, query: &str) -> Response

Handle GET /authorize - redirect to the upstream authorize URL.

Forwards all OAuth query parameters (response_type, client_id, redirect_uri, scope, state, code_challenge, code_challenge_method) to the upstream identity provider. The upstream provider (e.g. Keycloak) presents the login UI and redirects the user back to the MCP client’s redirect_uri with an authorization code.