Build the upstream authorization redirect URL for a proxied /authorize
request. The proxy substitutes its OWN fixed upstream client_id and fixed
callback URL, forwarding the client-supplied PKCE code_challenge, scope,
state, and (RFC 8707) resource. The client's real redirect_uri is NOT sent
upstream — the proxy receives the code at its fixed callback and relays it.
Build the upstream authorization redirect URL for a proxied /authorize request. The proxy substitutes its OWN fixed upstream client_id and fixed callback URL, forwarding the client-supplied PKCE code_challenge, scope, state, and (RFC 8707) resource. The client's real redirect_uri is NOT sent upstream — the proxy receives the code at its fixed callback and relays it.