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deps/curl/docs/libcurl/opts/CURLOPT_PROXY_PINNEDPUBLICKEY.md

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+---
+c: Copyright (C) Daniel Stenberg, <daniel.se>, et al.
+SPDX-License-Identifier: curl
+Title: CURLOPT_PROXY_PINNEDPUBLICKEY
+Section: 3
+Source: libcurl
+See-also:
+  - CURLOPT_PINNEDPUBLICKEY (3)
+  - CURLOPT_PROXY_CAINFO (3)
+  - CURLOPT_PROXY_CAPATH (3)
+  - CURLOPT_PROXY_SSL_VERIFYHOST (3)
+  - CURLOPT_PROXY_SSL_VERIFYPEER (3)
+---
+
+# NAME
+
+CURLOPT_PROXY_PINNEDPUBLICKEY - pinned public key for https proxy
+
+# SYNOPSIS
+
+~~~c
+#include <curl/curl.h>
+
+CURLcode curl_easy_setopt(CURL *handle, CURLOPT_PROXY_PINNEDPUBLICKEY,
+                          char *pinnedpubkey);
+~~~
+
+# DESCRIPTION
+
+Pass a pointer to a null-terminated string as parameter. The string can be the
+filename of your pinned public key. The file format expected is "PEM" or
+"DER". The string can also be any number of base64 encoded sha256 hashes
+preceded by "sha256//" and separated by ";"
+
+When negotiating a TLS or SSL connection, the https proxy sends a certificate
+indicating its identity. A public key is extracted from this certificate and
+if it does not exactly match the public key provided to this option, libcurl
+aborts the connection before sending or receiving any data.
+
+On mismatch, *CURLE_SSL_PINNEDPUBKEYNOTMATCH* is returned.
+
+The application does not have to keep the string around after setting this
+option.
+
+# DEFAULT
+
+NULL
+
+# PROTOCOLS
+
+All TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc.
+
+# EXAMPLE
+
+~~~c
+int main(void)
+{
+  CURL *curl = curl_easy_init();
+  if(curl) {
+    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
+    curl_easy_setopt(curl, CURLOPT_PROXY, "https://proxy:443");
+    curl_easy_setopt(curl, CURLOPT_PROXY_PINNEDPUBLICKEY,
+                     "sha256//YhKJKSzoTt2b5FP18fvpHo7fJYqQCjA"
+                     "a3HWY3tvRMwE=;sha256//t62CeU2tQiqkexU74"
+                     "Gxa2eg7fRbEgoChTociMee9wno=");
+
+    /* Perform the request */
+    curl_easy_perform(curl);
+  }
+}
+~~~
+
+# PUBLIC KEY EXTRACTION
+
+If you do not have the https proxy server's public key file you can extract it
+from the https proxy server's certificate.
+~~~c
+# retrieve the server's certificate if you do not already have it
+#
+# be sure to examine the certificate to see if it is what you expected
+#
+# Windows-specific:
+# - Use NUL instead of /dev/null.
+# - OpenSSL may wait for input instead of disconnecting. Hit enter.
+# - If you do not have sed, then just copy the certificate into a file:
+#   Lines from -----BEGIN CERTIFICATE----- to -----END CERTIFICATE-----.
+#
+openssl s_client -servername www.example.com -connect www.example.com:443 \
+  < /dev/null | sed -n "/-----BEGIN/,/-----END/p" > www.example.com.pem
+
+# extract public key in pem format from certificate
+openssl x509 -in www.example.com.pem -pubkey -noout > www.example.com.pubkey.pem
+
+# convert public key from pem to der
+openssl asn1parse -noout -inform pem -in www.example.com.pubkey.pem \
+  -out www.example.com.pubkey.der
+
+# sha256 hash and base64 encode der to string for use
+openssl dgst -sha256 -binary www.example.com.pubkey.der | openssl base64
+~~~
+The public key in PEM format contains a header, base64 data and a
+footer:
+~~~c
+-----BEGIN PUBLIC KEY-----
+[BASE 64 DATA]
+-----END PUBLIC KEY-----
+~~~
+
+# AVAILABILITY
+
+PEM/DER support:
+
+ 7.52.0: GnuTLS, OpenSSL, mbedTLS, wolfSSL
+
+sha256 support:
+
+ 7.52.0: GnuTLS, OpenSSL, mbedTLS, wolfSSL
+
+Other SSL backends not supported.
+
+# RETURN VALUE
+
+Returns CURLE_OK if TLS enabled, CURLE_UNKNOWN_OPTION if not, or
+CURLE_OUT_OF_MEMORY if there was insufficient heap space.