title: .Net Core behind NGINX returns 502 Bad Gateway after authentication by IdentityServer4
body: <p>Having two applications <strong>auth</strong> and <strong>store</strong> and authenticating using IdentityServer4 and both are behind NGINX.</p>
  
  <p>The store application successfully authenticates but after coming back from the auth application we get 502 Bad Gateway from NGINX.</p>
  
  <p>Any idea what is going wrong here?</p>
  
  <p>Auth app log:</p>
  
  <pre><code>info: Microsoft.AspNetCore.Hosting.Internal.WebHost[2]
        Request finished in 117.7292ms 200 text/html; charset=UTF-8
  info: Microsoft.AspNetCore.Hosting.Internal.WebHost[1]
        Request starting HTTP/1.0 POST http://auth.example.com/connect/token application/x-www-form-urlencoded 279
  info: IdentityServer4.Hosting.IdentityServerMiddleware[0]
        Invoking IdentityServer endpoint: IdentityServer4.Endpoints.TokenEndpoint for /connect/token
  info: IdentityServer4.Validation.TokenRequestValidator[0]
        Token request validation success
        {
          "ClientId": "ExampleStore",
          "ClientName": "Example Web Store",
          "GrantType": "authorization_code",
          "AuthorizationCode": "6fab1723...",
          "Raw": {
            "client_id": "ExampleStore",
            "client_secret": "***REDACTED***",
            "code": "6fab1723...",
            "grant_type": "authorization_code",
            "redirect_uri": "https://store.example.com/signin-oidc"
          }
        }
  info: Microsoft.AspNetCore.Hosting.Internal.WebHost[2]
        Request finished in 182.8022ms 200 application/json; charset=UTF-8
  info: Microsoft.AspNetCore.Hosting.Internal.WebHost[1]
        Request starting HTTP/1.0 GET http://auth.example.com/connect/userinfo
  info: IdentityServer4.Hosting.IdentityServerMiddleware[0]
        Invoking IdentityServer endpoint: IdentityServer4.Endpoints.UserInfoEndpoint for /connect/userinfo
  info: IdentityServer4.ResponseHandling.UserInfoResponseGenerator[0]
        Profile service returned to the following claim types: sub preferred_username name
  info: Microsoft.AspNetCore.Hosting.Internal.WebHost[2]
        Request finished in 57.1394ms 200 application/json; charset=UTF-8
  </code></pre>
  
  <p>Store app log:</p>
  
  <pre><code>info: Microsoft.AspNetCore.Authorization.DefaultAuthorizationService[2]
        Authorization failed for user: (null).
  info: Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker[3]
        Authorization failed for the request at filter 'Microsoft.AspNetCore.Mvc.Authorization.AuthorizeFilter'.
  info: Microsoft.AspNetCore.Mvc.ChallengeResult[1]
        Executing ChallengeResult with authentication schemes ().
  info: Microsoft.AspNetCore.Authentication.OpenIdConnect.OpenIdConnectHandler[12]
        AuthenticationScheme: oidc was challenged.
  info: Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker[2]
        Executed action Nihonto.Web.Store.Controllers.UserController.Login (Nihonto.Web.Store) in 8.1968ms
  info: Microsoft.AspNetCore.ResponseCaching.ResponseCachingMiddleware[27]
        The response could not be cached for this request.
  info: Microsoft.AspNetCore.Hosting.Internal.WebHost[2]
        Request finished in 11.2816ms 302
  info: Microsoft.AspNetCore.Hosting.Internal.WebHost[1]
        Request starting HTTP/1.0 POST http://store.example.com/signin-oidc application/x-www-form-urlencoded 1485
  info: Microsoft.AspNetCore.Authentication.Cookies.CookieAuthenticationHandler[10]
        AuthenticationScheme: ExampleCookie signed in.
  info: Microsoft.AspNetCore.Hosting.Internal.WebHost[2]
        Request finished in 301.361ms 302
  </code></pre>
  
  <p>More information of this issue can be found here : <a href="https://github.com/IdentityServer/IdentityServer4/issues/2101" rel="noreferrer">https://github.com/IdentityServer/IdentityServer4/issues/2101</a></p>