Getting SSL certificate info on a reused connection

From: Jicea via curl-library <curl-library_at_lists.haxx.se>
Date: Mon, 8 Jul 2024 12:41:58 +0000

Hi all,

I would like to get SSL certificate information by using CURLINFO_CERTINFO.

On a simple configuration (classic libcurl sample), I can get the information I need on the SSL certs chain.
If I'm doing a second call with the same curl handle and if the connection is reused, CURLINFO_CERTINFO doesn't provide any SSL certificate.

Looking at the logs, I can see, for instance:

==================* Found bundle for host: 0x600003d80b40 [can multiplex]
* Re-using existing connection with host google.com
* [HTTP/2] [3] OPENED stream for https://google.com/
* [HTTP/2] [3] [:method: GET]
* [HTTP/2] [3] [:scheme: https]
* [HTTP/2] [3] [:authority: google.com]
* [HTTP/2] [3] [:path: /]
* [HTTP/2] [3] [accept: */*]
> GET / HTTP/2

I've the impression that, as the connection is reused, and the SSL handshake doesn't occur the second time, CURLINFO_CERTINFO doesn't convey any certificates to look.

Can somebody confirms this?

What could I do to get these certificates information, regardless of the connection is reused or not? I'm thinking about keeping a "cache" of certificates info on the client side but I fear bad side effects (bug on my parts!)
(or just a map of connection-id / certificates)



My libcurl C sample:

```
#include <stdio.h>
#include <curl/curl.h>

void print_cert(CURL* curl) {
    int i;
    struct curl_certinfo *ci;
    CURLcode res = curl_easy_getinfo(curl, CURLINFO_CERTINFO, &ci);
    if (res) {
        fprintf(stderr, "Error calling CURLINFO_CERTINFO");
        return;
    }

    fprintf(stderr, "%d certs!\n", ci->num_of_certs);

    for (i = 0; i < ci->num_of_certs; i++) {
        struct curl_slist *slist;

        for (slist = ci->certinfo[i]; slist; slist = slist->next)
            fprintf(stderr, "%s\n", slist->data);
    }
}

int main(void) {
    CURL *curl = curl_easy_init();
    if (!curl) {
        return 1;
    }
    CURLcode res;
    curl_easy_setopt(curl, CURLOPT_URL, "https://google.com");

    curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 0L);
    curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, 0L);
    curl_easy_setopt(curl, CURLOPT_CERTINFO, 1L);
    curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);

    fprintf(stderr, "==================");

    res = curl_easy_perform(curl);
    if (!res) {
        print_cert(curl);
    }

    fprintf(stderr, "==================");

    res = curl_easy_perform(curl);
    if (!res) {
        print_cert(curl);
    }

    curl_easy_cleanup(curl);
}
```

This will make 2 GET requests to "https://googl.com"

When executing:

```
$ ./main 2>&1 >/dev/null | grep certs
3 certs!
0 certs!
```

Thanks a lot!








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Received on 2024-07-08