Added description for the clientError

Author: Catalina Turlea

Sources/Base/OAuth2Error.swift

@@ -275,6 +275,8 @@ public enum OAuth2Error: Error, CustomStringConvertible, Equatable {
 			return message ?? "The requested scope is invalid, unknown, or malformed."
 		case .serverError:
 			return "The authorization server encountered an unexpected condition that prevented it from fulfilling the request."
+		case .clientError(let statusCode):
+			return "The authorization server returned \(statusCode)"
 		case .temporarilyUnavailable(let message):
 			return message ?? "The authorization server is currently unable to handle the request due to a temporary overloading or maintenance of the server."
 		case .invalidGrant(let message):