Fix #1442

Author: yhirose

httplib.h

@@ -255,6 +255,8 @@ using socket_t = int;
 
 #if OPENSSL_VERSION_NUMBER < 0x1010100fL
 #error Sorry, OpenSSL versions prior to 1.1.1 are not supported
+#elif OPENSSL_VERSION_NUMBER < 0x30000000L
+#define SSL_get1_peer_certificate SSL_get_peer_certificate
 #endif
 
 #endif
@@ -7716,7 +7718,7 @@ inline bool SSLClient::initialize_ssl(Socket &socket, Error &error) {
             return false;
           }
 
-          auto server_cert = SSL_get_peer_certificate(ssl2);
+          auto server_cert = SSL_get1_peer_certificate(ssl2);
 
           if (server_cert == nullptr) {
             error = Error::SSLServerVerification;