title: Azure - AD - AcquireTokenSilent giving error failed_to_acquire_token_silently
body: <p>We are using Azure AD to authenticate and get the refreshed access token every 30 mins. We invoke below method which acquires security token and add it to request header.</p>
  
  <pre><code>var userObjectId = ClaimsPrincipal.Current.FindFirst("http://schemas.microsoft.com/identity/claims/objectidentifier").Value;
  var authContext = new AuthenticationContext(Authority, new NaiveSessionCache(userObjectId));
  var credential = new ClientCredential(ConfigurationManager.AppSettings["ida:ClientId"],
  ConfigurationManager.AppSettings["ida:ClientSecret"]);
  
      try
      {
      var authenticationResult = authContext.AcquireTokenSilent(ConfigurationManager.AppSettings["WebAPIBaseAddress"], credential, new UserIdentifier(userObjectId, UserIdentifierType.UniqueId));
      //set cookie for azure oauth refresh token - on successful login
      var httpCookie = HttpContext.Current.Response.Cookies["RefreshToken"];
      if (httpCookie != null)
          httpCookie.Value = authenticationResult.RefreshToken;
  
      request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", authenticationResult.AccessToken);
      }
      catch
      {
      //Get access token using Refresh Token 
      var authenticationResult = authContext.AcquireTokenByRefreshToken(httpCookie.Value, credential, ConfigurationManager.AppSettings["WebAPIBaseAddress"]);
      }
  </code></pre>
  
  <p>In above method, we have used AcquireTokenSilent method which gives us access token. Since access token lasts only for certain period of time.
  After its expiry, we call AcquireTokenByRefreshToken to get refresh token.</p>
  
  <p>The above code works well, however we are getting below exception randomly:</p>
  
  <pre><code>Microsoft.IdentityModel.Clients.ActiveDirectory.AdalSilentTokenAcquisitionException: Failed to acquire token silently. Call method AcquireToken 
     at Microsoft.IdentityModel.Clients.ActiveDirectory.AcquireTokenSilentHandler.SendTokenRequestAsync() 
     at Microsoft.IdentityModel.Clients.ActiveDirectory.AcquireTokenHandlerBase.&lt;RunAsync&gt;d__0.MoveNext()
  ErrorCode: failed_to_acquire_token_silently
  </code></pre>
  
  <p>What could be the reason of such inconsistent behaviour? The same code is working on few environments (Stage/Dev) but its throwing error randomly on Production.</p>
  
  <p>Please suggest.</p>