result = authContext.AcquireTokenAsync(resourceHostUri, clientId, new UserCredential(hardcodedUsername, hardcodedPassword)).Result;

string hardcodedUsername = "username";
        string hardcodedPassword = "password";

        string tenant = "tenantId@onmicrosoft.com";
        string clientId = "clientId";
        string resourceHostUri = "https://management.azure.com/";
        string aadInstance = "https://login.microsoftonline.com/{0}";

        string authority = String.Format(CultureInfo.InvariantCulture, aadInstance, tenant);


        authContext = new AuthenticationContext(authority);

        AuthenticationResult result = null;
            try
            {

                result = authContext.AcquireTokenAsync(resourceHostUri, clientId, new UserCredential(hardcodedUsername, hardcodedPassword)).Result;
            }
            catch (Exception ex)
            {
                System.Diagnostics.Debug.WriteLine(ex.Message);
            }

            return result;

// Get OAuth token using client credentials
string tenantName = "GraphDir1.OnMicrosoft.com";
string authString = "https://login.microsoftonline.com/" + tenantName;

AuthenticationContext authenticationContext = new AuthenticationContext(authString, false);

// Config for OAuth client credentials
string clientId = "118473c2-7619-46e3-a8e4-6da8d5f56e12";
string key = "hOrJ0r0TZ4GQ3obp+vk3FZ7JBVP+TX353kNo6QwNq7Q=";
ClientCredential clientCred = new ClientCredential(clientId, key);
string resource = "https://graph.windows.net";
string token;
try
{
    AuthenticationResult authenticationResult = authenticationContext.AcquireToken(resource, clientCred);
    token = authenticationResult.AccessToken;
}
catch (AuthenticationException ex)
{
    Console.ForegroundColor = ConsoleColor.Red;
    Console.WriteLine("Acquiring a token failed with the following error: {0}", ex.Message);
    if (ex.InnerException != null)
    {
        //  You should implement retry and back-off logic according to
        //  http://msdn.microsoft.com/en-us/library/dn168916.aspx . This topic also
                                //  explains the HTTP error status code in the InnerException message.
        Console.WriteLine("Error detail: {0}", ex.InnerException.Message);
    }
}

static void Main(string[] args)
    {
        Task<AuthenticationResult> t = getAccessToken();
        t.Wait();
        var result = t.Result;
        Console.WriteLine(result.AccessToken);
        Console.WriteLine("Please any key to terminate the program");
        Console.ReadKey();
    }

    public static async Task<AuthenticationResult> getAccessToken()
    {
        string hardcodedUsername = "username";
        string hardcodedPassword = "password";

        string tenant = "tenant.onmicrosoft.com";
        string clientId = "clientId";
        string resourceHostUri = "https://management.azure.com/";
        string aadInstance = "https://login.microsoftonline.com/{0}";

        string authority = String.Format(CultureInfo.InvariantCulture, aadInstance, tenant);


        var authContext = new AuthenticationContext(authority);

        AuthenticationResult result = null;
        try
        {
            result = await authContext.AcquireTokenAsync(resourceHostUri, clientId, new UserCredential(hardcodedUsername, hardcodedPassword));
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.StackTrace);
            System.Diagnostics.Debug.WriteLine(ex.Message);
        }

        return result;
    }