We can get cert information from the server by sending a HEAD request instead of get (-I) and showing more details (-v). Redirect the output from stderr to stdout, so we can use it with grep. Search for the cert keywords using extended regex (-E).
The response shows the CAfile referened by curl and server’s cert details such as the certificate chain and for whom the cert is issued for.
curl -vI https://jsonplaceholder.typicode.com/ 2>&1 | grep -E "(certificate|issuer|subject)"
* CAfile: /etc/ssl/certs/ca-certificates.crt
* Server certificate:
* subject: CN=typicode.com
* subjectAltName: host "jsonplaceholder.typicode.com" matched cert's "*.typicode.com"
* issuer: C=US; O=Google Trust Services; CN=WE1
* SSL certificate verify ok.