Inheritance: IGitHubAuthority
        /// <summary>
        ///
        /// </summary>
        /// <param name="tokenScope"></param>
        /// <param name="personalAccessTokenStore"></param>
        public GitHubAuthentication(
            GitHubTokenScope tokenScope,
            ICredentialStore personalAccessTokenStore,
            AcquireCredentialsDelegate acquireCredentialsCallback,
            AcquireAuthenticationCodeDelegate acquireAuthenticationCodeCallback,
            AuthenticationResultDelegate authenticationResultCallback)
        {
            if (tokenScope == null)
            {
                throw new ArgumentNullException("tokenScope", "The parameter `tokenScope` is null or invalid.");
            }
            if (personalAccessTokenStore == null)
            {
                throw new ArgumentNullException("personalAccessTokenStore", "The parameter `personalAccessTokenStore` is null or invalid.");
            }
            if (acquireCredentialsCallback == null)
            {
                throw new ArgumentNullException("acquireCredentialsCallback", "The parameter `acquireCredentialsCallback` is null or invalid.");
            }
            if (acquireAuthenticationCodeCallback == null)
            {
                throw new ArgumentNullException("acquireAuthenticationCodeCallback", "The parameter `acquireAuthenticationCodeCallback` is null or invalid.");
            }

            TokenScope = tokenScope;

            PersonalAccessTokenStore = personalAccessTokenStore;
            GitHubAuthority          = new GitHubAuthority();

            AcquireCredentialsCallback        = acquireCredentialsCallback;
            AcquireAuthenticationCodeCallback = acquireAuthenticationCodeCallback;
            AuthenticationResultCallback      = authenticationResultCallback;
        }
        /// <summary>
        /// <para></para>
        /// <para>Tokens acquired are stored in the secure secret store provided during
        /// initialization.</para>
        /// </summary>
        /// <param name="targetUri">The unique identifier for the resource for which access is to
        /// be acquired.</param>
        /// <param name="username">The username of the account for which access is to be acquired.</param>
        /// <param name="password">The password of the account for which access is to be acquired.</param>
        /// <param name="authenticationCode">The two-factor authentication code for use in access acquisition.</param>
        /// <returns>True if success; otherwise false.</returns>
        public async Task <bool> NoninteractiveLogonWithCredentials(TargetUri targetUri, string username, string password, string authenticationCode = null)
        {
            BaseSecureStore.ValidateTargetUri(targetUri);
            if (String.IsNullOrWhiteSpace(username))
            {
                throw new ArgumentNullException("username", "The `username` parameter is null or invalid.");
            }
            if (String.IsNullOrWhiteSpace(password))
            {
                throw new ArgumentNullException("username", "The `password` parameter is null or invalid.");
            }

            Trace.WriteLine("GitHubAuthentication::NoninteractiveLogonWithCredentials");

            GitHubAuthenticationResult result;

            if (result = await GitHubAuthority.AcquireToken(targetUri, username, password, authenticationCode, this.TokenScope))
            {
                Trace.WriteLine("   token acquisition succeeded");

                PersonalAccessTokenStore.WriteCredentials(targetUri, (Credential)result.Token);

                return(true);
            }

            Trace.WriteLine("   non-interactive logon failed");
            return(false);
        }
        /// <summary>
        ///
        /// </summary>
        /// <param name="tokenScope"></param>
        /// <param name="personalAccessTokenStore"></param>
        public GitHubAuthentication(
            GitHubTokenScope tokenScope,
            ICredentialStore personalAccessTokenStore,
            AcquireCredentialsDelegate acquireCredentialsCallback,
            AcquireAuthenticationCodeDelegate acquireAuthenticationCodeCallback,
            AuthenticationResultDelegate authenticationResultCallback)
        {
            if (tokenScope == null)
                throw new ArgumentNullException("tokenScope", "The parameter `tokenScope` is null or invalid.");
            if (personalAccessTokenStore == null)
                throw new ArgumentNullException("personalAccessTokenStore", "The parameter `personalAccessTokenStore` is null or invalid.");
            if (acquireCredentialsCallback == null)
                throw new ArgumentNullException("acquireCredentialsCallback", "The parameter `acquireCredentialsCallback` is null or invalid.");
            if (acquireAuthenticationCodeCallback == null)
                throw new ArgumentNullException("acquireAuthenticationCodeCallback", "The parameter `acquireAuthenticationCodeCallback` is null or invalid.");

            TokenScope = tokenScope;

            PersonalAccessTokenStore = personalAccessTokenStore;
            GitHubAuthority = new GitHubAuthority();

            AcquireCredentialsCallback = acquireCredentialsCallback;
            AcquireAuthenticationCodeCallback = acquireAuthenticationCodeCallback;
            AuthenticationResultCallback = authenticationResultCallback;
        }
        /// <summary>
        /// Validates that a set of credentials grants access to the target resource.
        /// </summary>
        /// <param name="targetUri">The unique identifier for the resource for which credentials
        /// are being validated against.</param>
        /// <param name="credentials">The credentials to validate.</param>
        /// <returns>True is successful; otherwise false.</returns>
        public async Task <bool> ValidateCredentials(TargetUri targetUri, Credential credentials)
        {
            BaseSecureStore.ValidateTargetUri(targetUri);
            BaseSecureStore.ValidateCredential(credentials);

            return(await GitHubAuthority.ValidateCredentials(targetUri, credentials));
        }
        /// <summary>
        /// <para></para>
        /// <para>Tokens acquired are stored in the secure secret store provided during
        /// initialization.</para>
        /// </summary>
        /// <param name="targetUri">The unique identifier for the resource for which access is to
        /// be acquired.</param>
        /// <param name="username">The username of the account for which access is to be acquired.</param>
        /// <param name="password">The password of the account for which access is to be acquired.</param>
        /// <param name="authenticationCode">The two-factor authentication code for use in access acquisition.</param>
        /// <returns>Acquired <see cref="Credential"/> if successful; otherwise <see langword="null"/>.</returns>
        public async Task <Credential> NoninteractiveLogonWithCredentials(TargetUri targetUri, string username, string password, string authenticationCode)
        {
            BaseSecureStore.ValidateTargetUri(targetUri);
            if (String.IsNullOrWhiteSpace(username))
            {
                throw new ArgumentNullException("username", "The `username` parameter is null or invalid.");
            }
            if (String.IsNullOrWhiteSpace(password))
            {
                throw new ArgumentNullException("username", "The `password` parameter is null or invalid.");
            }

            Credential credentials = null;

            GitHubAuthenticationResult result;

            if (result = await GitHubAuthority.AcquireToken(targetUri, username, password, authenticationCode, this.TokenScope))
            {
                Git.Trace.WriteLine($"token acquisition for '{targetUri}' succeeded.");

                credentials = (Credential)result.Token;
                PersonalAccessTokenStore.WriteCredentials(targetUri, credentials);

                return(credentials);
            }

            Git.Trace.WriteLine($"non-interactive logon for '{targetUri}' failed.");
            return(credentials);
        }
        /// <summary>
        /// <para></para>
        /// <para>Tokens acquired are stored in the secure secret store provided during
        /// initialization.</para>
        /// </summary>
        /// <param name="targetUri">The unique identifier for the resource for which access is to
        /// be acquired.</param>
        /// <param name="credentials">(out) Credentials when acquisition is successful; null otherwise.</param>
        /// <returns>True if success; otherwise false.</returns>
        public bool InteractiveLogon(TargetUri targetUri, out Credential credentials)
        {
            string username;
            string password;

            if (AcquireCredentialsCallback(targetUri, out username, out password))
            {
                GitHubAuthenticationResult result;

                if (result = GitHubAuthority.AcquireToken(targetUri, username, password, null, this.TokenScope).Result)
                {
                    Trace.WriteLine("   token acquisition succeeded");

                    credentials = (Credential)result.Token;
                    this.PersonalAccessTokenStore.WriteCredentials(targetUri, credentials);

                    // if a result callback was registered, call it
                    if (AuthenticationResultCallback != null)
                    {
                        AuthenticationResultCallback(targetUri, result);
                    }

                    return(true);
                }
                else if (result == GitHubAuthenticationResultType.TwoFactorApp ||
                         result == GitHubAuthenticationResultType.TwoFactorSms)
                {
                    string authenticationCode;
                    if (AcquireAuthenticationCodeCallback(targetUri, result, username, out authenticationCode))
                    {
                        if (result = GitHubAuthority.AcquireToken(targetUri, username, password, authenticationCode, this.TokenScope).Result)
                        {
                            Trace.WriteLine("   token acquisition succeeded");

                            credentials = (Credential)result.Token;
                            this.PersonalAccessTokenStore.WriteCredentials(targetUri, credentials);

                            // if a result callback was registered, call it
                            if (AuthenticationResultCallback != null)
                            {
                                AuthenticationResultCallback(targetUri, result);
                            }

                            return(true);
                        }
                    }
                }

                // if a result callback was registered, call it
                if (AuthenticationResultCallback != null)
                {
                    AuthenticationResultCallback(targetUri, result);
                }
            }

            Trace.WriteLine("   interactive logon failed");
            credentials = null;
            return(false);
        }
        /// <summary>
        /// Validates that a set of credentials grants access to the target resource.
        /// </summary>
        /// <param name="targetUri">The unique identifier for the resource for which credentials
        /// are being validated against.</param>
        /// <param name="credentials">The credentials to validate.</param>
        /// <returns>True is successful; otherwise false.</returns>
        public async Task <bool> ValidateCredentials(TargetUri targetUri, Credential credentials)
        {
            BaseSecureStore.ValidateTargetUri(targetUri);
            Credential.Validate(credentials);

            Trace.WriteLine("GitHubAuthentication::ValidateCredentials");

            return(await GitHubAuthority.ValidateCredentials(targetUri, credentials));
        }
        /// <summary>
        /// <para></para>
        /// <para>Tokens acquired are stored in the secure secret store provided during
        /// initialization.</para>
        /// </summary>
        /// <param name="targetUri">The unique identifier for the resource for which access is to
        /// be acquired.</param>
        /// /// <returns>Acquired <see cref="Credential"/> if successful; otherwise <see langword="null"/>.</returns>
        public async Task <Credential> InteractiveLogon(TargetUri targetUri)
        {
            Credential credentials = null;
            string     username;
            string     password;

            if (AcquireCredentialsCallback(targetUri, out username, out password))
            {
                GitHubAuthenticationResult result;

                if (result = await GitHubAuthority.AcquireToken(targetUri, username, password, null, this.TokenScope))
                {
                    Git.Trace.WriteLine($"token acquisition for '{targetUri}' succeeded");

                    credentials = (Credential)result.Token;
                    this.PersonalAccessTokenStore.WriteCredentials(targetUri, credentials);

                    // if a result callback was registered, call it
                    AuthenticationResultCallback?.Invoke(targetUri, result);

                    return(credentials);
                }
                else if (result == GitHubAuthenticationResultType.TwoFactorApp ||
                         result == GitHubAuthenticationResultType.TwoFactorSms)
                {
                    string authenticationCode;
                    if (AcquireAuthenticationCodeCallback(targetUri, result, username, out authenticationCode))
                    {
                        if (result = await GitHubAuthority.AcquireToken(targetUri, username, password, authenticationCode, this.TokenScope))
                        {
                            Git.Trace.WriteLine($"token acquisition for '{targetUri}' succeeded.");

                            credentials = (Credential)result.Token;
                            this.PersonalAccessTokenStore.WriteCredentials(targetUri, credentials);

                            // if a result callback was registered, call it
                            AuthenticationResultCallback?.Invoke(targetUri, result);

                            return(credentials);
                        }
                    }
                }

                // if a result callback was registered, call it
                if (AuthenticationResultCallback != null)
                {
                    AuthenticationResultCallback(targetUri, result);
                }
            }

            Git.Trace.WriteLine($"interactive logon for '{targetUri}' failed.");
            return(credentials);
        }