title: "Error unprotecting the session cookie" exception
body: <p>i have an Asp.NET MVC application with this Authentication setup:</p>
  
  <p>ConfigureServices():</p>
  
  <pre><code>services.AddSession()
  services.AddAuthentication(sharedOptions =&gt; sharedOptions.SignInScheme = CookieAuthenticationDefaults.AuthenticationScheme);
  </code></pre>
  
  <p>Configure():</p>
  
  <pre><code>        app.UseCookieAuthentication(new CookieAuthenticationOptions());
          app.UseOpenIdConnectAuthentication(new OpenIdConnectOptions
          {
              ClientId = "xx",
              Authority = "xx",
              Events = new OpenIdConnectEvents { OnRemoteFailure = this.OnAuthenticationFailed }
          });
  </code></pre>
  
  <p>When hosted in IIS, some users get this exception:</p>
  
  <pre><code>Microsoft.AspNetCore.Session.SessionMiddleware, 
        Error unprotecting the session cookie.
  System.Security.Cryptography.CryptographicException: The key {9ec59def-874e-45df-9bac-d629f5716a04} was not found in the key ring.
     at Microsoft.AspNetCore.DataProtection.KeyManagement.KeyRingBasedDataProtector.UnprotectCore(Byte[] protectedData, Boolean allowOperationsOnRevokedKeys, UnprotectStatus&amp; status)
     at Microsoft.AspNetCore.DataProtection.KeyManagement.KeyRingBasedDataProtector.DangerousUnprotect(Byte[] protectedData, Boolean ignoreRevocationErrors, Boolean&amp; requiresMigration, Boolean&amp; wasRevoked)
     at Microsoft.AspNetCore.DataProtection.KeyManagement.KeyRingBasedDataProtector.Unprotect(Byte[] protectedData)
     at Microsoft.AspNetCore.Session.CookieProtection.Unprotect(IDataProtector protector, String protectedText, ILogger logger)
  </code></pre>
  
  <p>I have run this on the hosting server <a href="https://github.com/aspnet/DataProtection/blob/dev/Provision-AutoGenKeys.ps1" rel="noreferrer">https://github.com/aspnet/DataProtection/blob/dev/Provision-AutoGenKeys.ps1</a></p>
  
  <p>Web has only HTTPS binding, SSL certificate is ok and signed. What might cause this issue? What actually is that "key" value?</p>