Provided the value of an "Authorization" header, you will get a bool result and the username and password if successful.

BasicAuthentication.cs

public static bool TryParseBasicAuthentication(string header, out string username, out string password)
{
    username = null; password = null;

    try
    {
        if (!header.StartsWith("Basic "))
            return false;

        // Remove the scheme and optional space after colon if present.
        header = header.Replace("Basic", "").TrimStart();

        Encoding encoding = Encoding.GetEncoding("iso-8859-1");
        const char separator = ':';
        string unencodedAuth = encoding.GetString(Convert.FromBase64String(header));

        if (!unencodedAuth.Contains(separator))
            return false;

        int separatorIndex = unencodedAuth.IndexOf(separator);
        username = unencodedAuth.Substring(0, separatorIndex);
        password = unencodedAuth.Substring(separatorIndex + 1);

        return true;
    }
    catch
    {
        return false;
    }
}