The fhir client has two events available OnBeforeRequest and OnAfterResponse that you can subscribe to. In these events you can manipulate the outgoing request so you can bind a certificate there!
Using the Events ‘OnBeforeRequest’ i was able to now connect to the Server implementing the following 2 things:
pushed my certificate into my request
set the SecurityProtocolType to Tls12, because my Server ist only supporting this protocol type
…
//1.
X509Certificate2 clientCert2 = getCertificate();
if (clientCert2 != null)
{
e.RawRequest.ClientCertificates.Clear();
e.RawRequest.ClientCertificates.Add(clientCert2);
}