Leszek

The matter has been clarified. I used help The Embarcadero Support Customer Portal, rest client need to be changed. TOAuth2Authenticator uses its own client connection. He does not have access to the OnNeedClientCertificate event.

There was indeed a lack of parent certificates. I installed these certificates but the problem still persists While debugging, I noticed that when I enter the DoNeedClientCertificate method in System.Net.HttpClient, the condition is checked if Assigned(FNeedClientCertificateCallback) or Assigned(FNeedClientCertificateEvent) then begin DoGetClientCertificates(LRequest, LClientCertificateList); ... end; but FNeedClientCertificateCallback is nil FNeedClientCertificateEvent is nil so the DoGetClientCertificates method does not read the certificate list I will continue to debug the issue.

@Lars Fosdal You're right, sorry, I'll improve This is a government service, it works in a separate network, without external access. I don't use Indy, I use REST Client Library and components TRESTClient, TRESTRequest, TRESTResponse, TRESTResponseDataSetAdapter, TOAuth2Autenticator grant_type is set to client_credentials and I have to use a certificate. I can't use REST_Debugger because it doesn't deal with client_credentials. I get an error when connecting ERESTException REST request failed: Error sending data: (12175) which means a security error has occurred During the connection, the RESTClient.OnNeedClientCertificate event in which you specify the certificate is not executed. I do not know why.

Hello everyone Let me join in on this problem I am working on a Delphi (12.1) I am creating a rest client with TOAuth2Authenticator (client_credentials) and authorization with client certificates. The certificate is located in the windows certificate store in the right place, my problem is that the RESTClient.OnNeedClientCertificate event does not execute. I tried setting the properties ClientCertificatePath and ClientCertificatePassword in RESTClient but without any effects. Embarcadero reports that TRestClient supports using certificates from the local machine list and not only from the current user list. Do you have any idea how to solve this problem?