HttpContext httpContext = HttpContext.Current;

string authHeader = this.httpContext.Request.Headers["Authorization"];

if (authHeader != null && authHeader.StartsWith("Basic")) {
    string encodedUsernamePassword = authHeader.Substring("Basic ".Length).Trim();
    Encoding encoding = Encoding.GetEncoding("iso-8859-1");
    string usernamePassword = encoding.GetString(Convert.FromBase64String(encodedUsernamePassword));

    int seperatorIndex = usernamePassword.IndexOf(':');

    var username = usernamePassword.Substring(0, seperatorIndex);
    var password = usernamePassword.Substring(seperatorIndex + 1);
} else {
    //Handle what happens if that isn't the case
    throw new Exception("The authorization header is either empty or isn't Basic.");
}