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+---
+c: Copyright (C) Daniel Stenberg, <daniel.se>, et al.
+SPDX-License-Identifier: curl
+Title: CURLOPT_SSH_HOSTKEYFUNCTION
+Section: 3
+Source: libcurl
+See-also:
+  - CURLOPT_SSH_HOSTKEYDATA (3)
+  - CURLOPT_SSH_KNOWNHOSTS (3)
+---
+
+# NAME
+
+CURLOPT_SSH_HOSTKEYFUNCTION - callback to check host key
+
+# SYNOPSIS
+
+~~~c
+#include <curl/curl.h>
+
+int keycallback(void *clientp,
+                int keytype,
+                const char *key,
+                size_t keylen);
+
+CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSH_HOSTKEYFUNCTION,
+                          keycallback);
+~~~
+
+# DESCRIPTION
+
+Pass a pointer to your callback function, which should match the prototype
+shown above. It overrides CURLOPT_SSH_KNOWNHOSTS(3).
+
+This callback gets called when the verification of the SSH host key is needed.
+
+**key** is **keylen** bytes long and is the key to check. **keytype**
+says what type it is, from the **CURLKHTYPE_*** series in the
+**curl_khtype** enum.
+
+**clientp** is a custom pointer set with CURLOPT_SSH_HOSTKEYDATA(3).
+
+The callback MUST return one of the following return codes to tell libcurl how
+to act:
+
+## CURLKHMATCH_OK
+
+The host key is accepted, the connection should continue.
+
+## CURLKHMATCH_MISMATCH
+
+the host key is rejected, the connection is canceled.
+
+# DEFAULT
+
+NULL
+
+# PROTOCOLS
+
+SCP and SFTP
+
+# EXAMPLE
+
+~~~c
+struct mine {
+  void *custom;
+};
+
+int hostkeycb(void *clientp,    /* passed with CURLOPT_SSH_HOSTKEYDATA */
+              int keytype,      /* CURLKHTYPE */
+              const char *key,  /* host key to check */
+              size_t keylen)    /* length of the key */
+{
+  /* 'clientp' points to the callback_data struct */
+  /* investigate the situation and return the correct value */
+  return CURLKHMATCH_OK;
+}
+int main(void)
+{
+  struct mine callback_data;
+  CURL *curl = curl_easy_init();
+  if(curl) {
+    curl_easy_setopt(curl, CURLOPT_URL, "sftp://example.com/thisfile.txt");
+    curl_easy_setopt(curl, CURLOPT_SSH_HOSTKEYFUNCTION, hostkeycb);
+    curl_easy_setopt(curl, CURLOPT_SSH_HOSTKEYDATA, &callback_data);
+
+    curl_easy_perform(curl);
+  }
+}
+~~~
+
+# AVAILABILITY
+
+Added in 7.84.0 , work only with libssh2 backend.
+
+# RETURN VALUE
+
+Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.