Token request failed error when getting app only access token

Recently I started seeing token request failed error in my job and my provider hosted app.   The jobs and provided hosted apps have been working well for a long time and it just suddenly happened.  They always failed at TokenHelper.getAppOnlyAccessToken method.

Error info:

Type: System.Net.WebException

Message: Token request failed.

After digging around, it looks like there are a few updates on Microsoft to SharePoint, Azure, and AAD.  You can see more details from here, https://techcommunity.microsoft.com/t5/microsoft-sharepoint-blog/provider-hosted-app-pha-application-errors-tls-errors-and-401/ba-p/2273611.

Essentially, here are the 2 solution depending where is your code located:

• If you're running your jobs or web applications on a server, you can apply the change to update the TLS and cipher used.  See the details for the TLS/Cipher changes in the link above.
• If you're hosting the provided hosted app in Azure web app, you can update your code instead.  You can add ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12 to your code before you get the AppOnly access token.

Sample code:

public ClientContext GetAppContext() 

{

    ServicePointManager.SecurityPortocol = SecurityProtocolType.Tls12;

    Uri siteUri = new Uri(_sharepointUrl);    

    string realm = TokenHelper.GetRealmFromTargetUrl(siteUri);




    string accessToken = TokenHelper.GetAppOnlyAccessToken(

        TokeHelper.SharePointPrincipal, 

        siteUri.Authority, realm).AccessToken;




    return TokenHelper.GetClientContextWithAccessToken(siteUri.ToString(), accessToken);

}

after I added the yellow highlighted line, it started working on Azure web app.  That force the code to use TLS 1.2.