Redirect to React consent page.

Query Parameters (handled by Authlib): client_id: OAuth client identifier redirect_uri: Where to redirect after authorization response_type: Must be 'code' scope: Space-separated list of requested scopes state: CSRF protection token (optional but recommended) code_challenge: PKCE code challenge code_challenge_method: PKCE method (usually 'S256')

Returns: Redirect to React consent page with OAuth params and client info