Extract certificate from HTTPS site

Question

I need to extract the public key (preferably in PEM format) that a site uses to identify itself with.

E.g. a function that takes a URL as an argument (https://www.example.com/), then establish a connection to that site and fetches the certificate.

Any ideas about how it could be solved with PHP code?

Answer 1

You could use openssl to extract the certificate.

openssl s_client -connect google.com:443 > file.txt

You will find the certificate in file.txt between -----BEGIN CERTIFICATE----- and -----END CERTIFICATE-----, and you can extract it from there. I don't see a way to use the PHP OpenSSL module to do this from within PHP though, unfortunately.