Function build_auth_url 

pub fn build_auth_url(
    spec: &ProviderOAuthSpec,
    port: u16,
    state: &str,
    code_challenge: &str,
) -> String

Build the authorization URL for the OAuth authorization_code flow.

port is the local-loopback port the CLI has bound to capture the provider’s redirect — providers will reject the call if the redirect_uri host:port does not match a registered value, so it must be threaded through (not assumed to be 0).