System.Net.Http.Headers.AuthenticationHeaderValue.GetAuthenticationLength C# (CSharp) Method

        internal static int GetAuthenticationLength(string input, int startIndex, out object parsedValue)
        {
            Debug.Assert(startIndex >= 0);

            parsedValue = null;

            if (string.IsNullOrEmpty(input) || (startIndex >= input.Length))
            {
                return 0;
            }

            // Parse the scheme string: <scheme> in '<scheme> <parameter>'
            int schemeLength = HttpRuleParser.GetTokenLength(input, startIndex);

            if (schemeLength == 0)
            {
                return 0;
            }

            AuthenticationHeaderValue result = new AuthenticationHeaderValue();
            result._scheme = input.Substring(startIndex, schemeLength);

            int current = startIndex + schemeLength;
            int whitespaceLength = HttpRuleParser.GetWhitespaceLength(input, current);
            current = current + whitespaceLength;

            if ((current == input.Length) || (input[current] == ','))
            {
                // If we only have a scheme followed by whitespace, we're done.
                parsedValue = result;
                return current - startIndex;
            }

            // We need at least one space between the scheme and parameters. If there are no whitespace, then we must
            // have reached the end of the string (i.e. scheme-only string).
            if (whitespaceLength == 0)
            {
                return 0;
            }

            // If we get here, we have a <scheme> followed by a whitespace. Now we expect the following:
            // '<scheme> <blob>[,<name>=<value>]*[, <otherscheme>...]*': <blob> potentially contains one 
            // or more '=' characters, optionally followed by additional name/value pairs, optionally followed by 
            // other schemes. <blob> may be a quoted string.
            // We look at the value after ',': if it is <token>=<value> then we have a parameter for <scheme>.
            // If we have either a <token>-only or <token><whitespace><blob> then we have another scheme.
            int parameterStartIndex = current;
            int parameterEndIndex = current;
            if (!TrySkipFirstBlob(input, ref current, ref parameterEndIndex))
            {
                return 0;
            }

            if (current < input.Length)
            {
                if (!TryGetParametersEndIndex(input, ref current, ref parameterEndIndex))
                {
                    return 0;
                }
            }

            result._parameter = input.Substring(parameterStartIndex, parameterEndIndex - parameterStartIndex + 1);
            parsedValue = result;
            return current - startIndex;
        }