A little notes from the field, I recently saw this issue at a customer. Their ADFS Proxy (Active Directory Federation Service) was suddenly not working anymore, It had been running without issues for months.
When started to troubleshoot this, we looking at the Web Application Proxy (WAP) service on the ADFS Proxy server and the error we got was:
The operation stopped due to an unknown general error. Error code 0x8007520C.
We confirmed that the Web Applicaton Proxy service was stopped and the service could not be started. I suspected an issue with the certificate, since the ADFS is highly dependent on certificates working correctly.
To get a list of the certificates installed on the server, use the command via PowerShell:
The public certificate needed for the ADFS and it’s thumbprint is highlighted above with yellow marker. The thumbprint is then used for installing and configuring the Web Application Proxy with the correct certificate, which it done using the following command in PowerShell:
Install-WebApplicationProxy –CertificateThumbprint ThumbPrintFromCertificate –FederationServiceName fs.TopLevelDomain.dk
The Web Application Proxy service was then checked and it was now started and running.
The we tested the ADFS to confirm everything was working, you can test ADFS logon using the URL:
Everything now worked.