Checking a Certificate for the Subject

Subject: C=US, O=IBM Corporation, OU=IBM Watson Health
Subject Public Key Info:```

Checking TLS

openssl s_client -connect localhost:9443 -cert fhir.crt -key \
    fhir.key -state -debug
Enter pass phrase for fhir.key:
CONNECTED(00000005)
SSL_connect:before/connect initialization

The above shows that the client connected, and the details on the connection.

Details on the certificate

 openssl x509 -in fhiruser.crt -text

You can always use mutual-tls from cURL

curl --key fhiruser.key --cert fhiruser.crt -k -v \ 
    -u "fhiruser:change-password" \
    -H 'Content-Type: application/fhir+json' \
    'https://localhost:9443/fhir-server/api/v4/$import' 

Thanks to https://downey.io/notes/dev/curl-using-mutual-tls/