protected abstract Task AuthenticateAsync()

in API/Filters/BasicAuthenticationAttribute.cs [72:122]
38 lines of code
5 McCabe index (conditional complexity)

        protected abstract Task<IPrincipal> AuthenticateAsync(string userName, string password,
            CancellationToken cancellationToken);

        private static Tuple<string, string> ExtractUserNameAndPassword(string authorizationParameter)
        {
            byte[] credentialBytes;

            try
            {
                credentialBytes = Convert.FromBase64String(authorizationParameter);
            }
            catch (FormatException)
            {
                return null;
            }

            // The currently approved HTTP 1.1 specification says characters here are ISO-8859-1.
            // However, the current draft updated specification for HTTP 1.1 indicates this encoding is infrequently
            // used in practice and defines behavior only for ASCII.
            Encoding encoding = Encoding.ASCII;
            // Make a writable copy of the encoding to enable setting a decoder fallback.
            encoding = (Encoding)encoding.Clone();
            // Fail on invalid bytes rather than silently replacing and continuing.
            encoding.DecoderFallback = DecoderFallback.ExceptionFallback;
            string decodedCredentials;

            try
            {
                decodedCredentials = encoding.GetString(credentialBytes);
            }
            catch (DecoderFallbackException)
            {
                return null;
            }

            if (String.IsNullOrEmpty(decodedCredentials))
            {
                return null;
            }

            int colonIndex = decodedCredentials.IndexOf(':');

            if (colonIndex == -1)
            {
                return null;
            }

            string userName = decodedCredentials.Substring(0, colonIndex);
            string password = decodedCredentials.Substring(colonIndex + 1);
            return new Tuple<string, string>(userName, password);
        }