Add filter for alternative authorization header

inc/authentication/namespace.php

@@ -48,7 +48,28 @@ function get_authorization_header() {
 function get_provided_token() {
 	$header = get_authorization_header();
 	if ( $header ) {
-		return get_token_from_bearer_header( $header );
+		$token = get_token_from_bearer_header( $header );
+		if ( $token ) {
+			return $token;
+		}
+	}
+
+	/**
+	 * Provide an alternative authorization header value.
+	 *
+	 * Use this filter when the standard Authorization header is consumed by a
+	 * proxy or server layer (e.g. Imperva HTTP Basic Auth). Return the raw
+	 * header value (e.g. "Bearer <token>") to have it parsed as a bearer token.
+	 * Return null to skip the fallback entirely.
+	 *
+	 * @param string|null $header Raw header value, or null to skip.
+	 */
+	$alt_header = apply_filters( 'oauth2.authentication.alternative_authorization_header', null );
+	if ( $alt_header ) {
+		$token = get_token_from_bearer_header( $alt_header );
+		if ( $token ) {
+			return $token;
+		}
 	}
 
 	$token = get_token_from_request();