CURLOPT_PR...LCERT_BLOB(3)

💅 CURLOPT_PROXY_SSLCERT_BLOB(3) — like, the libcurl manual, but make it make sense

okay bestie, so this is a page out of the libcurl manual (section 3, the library functions girlies), and it's about handing curl your proxy client certificate straight from memory instead of making it go dig around in your filesystem. no cap, it's a whole vibe. let's get into it 🎀

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✨ NAME ✨

CURLOPT_PROXY_SSLCERT_BLOB — SSL proxy client certificate from memory blob 💖

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🌸 SYNOPSIS 🌸

#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_PROXY_SSLCERT_BLOB,
                          struct curl_blob *blob);

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🦋 DESCRIPTION 🦋

So what you're doing here is passing a pointer to a curl_blob structure — and that struct is literally just carrying around the info (a pointer and a size, that's it, that's the whole thing) about a memory block holding the binary data of the certificate you wanna use to connect to the HTTPS proxy. 🫶

Now, the format gossip:

• The format must be "P12" on Schannel.
• The format must be "P12" or "PEM" on OpenSSL.

And you gotta spell out that "P12" or "PEM" string yourself using CURLOPT_PROXY_SSLCERTTYPE(3). iykyk 💅

If the blob gets initialized with the flags member of struct curl_blob set to CURL_BLOB_COPY, then bestie, you do not have to keep that buffer around after setting this. curl copies it for you. iconic behavior honestly. ✨

Also lowkey important: this option is an alternative to CURLOPT_PROXY_SSLCERT(3) — except that one wants a filename as input instead. two different girls, same job. 💀

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🎀 DEFAULT 🎀

NULL

like, obviously. nothing's set until you set it, periodt.

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🌈 PROTOCOLS 🌈

This functionality affects all TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc. the whole secure squad. 🔥

⚠️ but heads up — this option works only with the following TLS backends: OpenSSL and Schannel. so do a lil vibe check on your backend before you come crying to me 😭

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🧚 EXAMPLE 🧚

here's the whole thing, copy it exactly bestie, don't freestyle:

extern char *certificateData; /* point to data */
extern size_t filesize; /* size of the data */

int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    CURLcode result;
    struct curl_blob blob;
    blob.data = certificateData;
    blob.len = filesize;
    blob.flags = CURL_BLOB_COPY;
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
    curl_easy_setopt(curl, CURLOPT_PROXY, "https://proxy.example");
    curl_easy_setopt(curl, CURLOPT_PROXY_SSLKEY, "key.pem");
    curl_easy_setopt(curl, CURLOPT_PROXY_KEYPASSWD, "s3cret");
    curl_easy_setopt(curl, CURLOPT_PROXY_SSLCERT_BLOB, &blob);
    result = curl_easy_perform(curl);
    curl_easy_cleanup(curl);
  }
}

see how blob.flags = CURL_BLOB_COPY is right there? that's the "you can let go of the buffer now" cheat code. we love a self-sufficient queen. 👑

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⭐ AVAILABILITY ⭐

Added in curl 7.71.0. so if you're on something ancient, that's a skill issue bestie, upgrade. 🙈

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💜 RETURN VALUE 💜

curl_easy_setopt(3) returns a CURLcode indicating success or error.

• CURLE_OK (0) means everything was OK 🎉
• non-zero means an error occurred — go check libcurl-errors(3) for the tea

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🍓 SEE ALSO 🍓

• CURLOPT_PROXY_SSLCERT(3)
• CURLOPT_PROXY_SSLCERTTYPE(3)
• CURLOPT_PROXY_SSLKEY(3)
• CURLOPT_SSLCERT_BLOB(3)

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and that's the page!! 🫶 this one came from libcurl, dated 2026-10-12 — so if you ever need to cite your sources, that's the receipt. now go forth and proxy with your certificate blob, main character. 💅✨🌸