CURLOPT\_SOCKS5\_AUTH(3) Library Functions Manual CURLOPT\_SOCKS5\_AUTH(3)

# [NAME](#NAME)

CURLOPT\_SOCKS5\_AUTH - methods for SOCKS5 proxy authentication

# [SYNOPSIS](#SYNOPSIS)

```
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SOCKS5_AUTH, long bitmask);
```

# [DESCRIPTION](#DESCRIPTION)

Pass a long as parameter, which is set to a bitmask, to tell libcurl which authentication method(s) are allowed for SOCKS5 proxy authentication. The only supported flags are *CURLAUTH\_BASIC*, which allows username/password authentication, and *CURLAUTH\_GSSAPI*, which allows GSS-API authentication. Set the actual username and password with the [*CURLOPT\_PROXYUSERPWD(3)*](/man/os/curl/CURLOPT_PROXYUSERPWD.3) option.

libcurl offers the SOCKS5 "no authentication" method in addition to the ones in the bitmask, and accepts it if the proxy selects it. *CURLAUTH\_NONE* is zero and therefore cannot be combined with the other flags; setting the bitmask to *CURLAUTH\_NONE* makes libcurl offer only the no authentication method.

Add *CURLAUTH\_ONLY* to the bitmask to require authentication. libcurl then does not offer the no authentication method, and rejects it with *CURLE\_PROXY* if the proxy selects it anyway. A connection that was set up without SOCKS5 authentication is also not reused for such a transfer. Setting *CURLAUTH\_ONLY* without *CURLAUTH\_BASIC* or *CURLAUTH\_GSSAPI* makes [*curl\_easy\_setopt(3)*](/man/os/curl/curl_easy_setopt.3) return *CURLE\_BAD\_FUNCTION\_ARGUMENT*.

The specific socks authentication method is an *access property*, it does not change the security context. This means that this option changes how the connection and access to the proxy happens when a connection is setup, but it does not affect which proxy connections libcurl can reuse. libcurl may reuse a connection that was set up with a different socks authentication method. Proxy connection reuse still depends on other properties matching, such as the protocol, proxy hostname, port number, credentials and other settings that affect the connection.

# [DEFAULT](#DEFAULT)

CURLAUTH\_BASIC | CURLAUTH\_GSSAPI

# [PROTOCOLS](#PROTOCOLS)

This functionality affects all supported protocols

# [EXAMPLE](#EXAMPLE)

```
int main(void)
{


  CURL *curl = curl_easy_init();


  if(curl) {


    CURLcode result;


    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");


    /* request to use a SOCKS5 proxy */


    curl_easy_setopt(curl, CURLOPT_PROXY, "socks5://user:pass@myproxy.com");


    /* enable username/password authentication only */


    curl_easy_setopt(curl, CURLOPT_SOCKS5_AUTH, CURLAUTH_BASIC);


    /* Perform the request */


    result = curl_easy_perform(curl);


    curl_easy_cleanup(curl);


  }
}
```

# [HISTORY](#HISTORY)

**CURLAUTH\_*** macros became *long* types in 7.26.0, prior to this version a *long* cast was necessary when passed to [*curl\_easy\_setopt(3)*](/man/os/curl/curl_easy_setopt.3).

*CURLAUTH\_ONLY* is supported since 8.23.0.

# [AVAILABILITY](#AVAILABILITY)

Added in curl 7.55.0

# [RETURN VALUE](#RETURN_VALUE)

[*curl\_easy\_setopt(3)*](/man/os/curl/curl_easy_setopt.3) returns a CURLcode indicating success or error.

CURLE\_OK (0) means everything was OK, non-zero means an error occurred, see [*libcurl-errors(3)*](/man/os/curl/libcurl-errors.3).

# [SEE ALSO](#SEE_ALSO)

[**CURLOPT\_PROXY**(3)](/man/os/curl/CURLOPT_PROXY.3), [**CURLOPT\_PROXYTYPE**(3)](/man/os/curl/CURLOPT_PROXYTYPE.3)

2026-10-14 libcurl

---

Document: CURLOPT_SOCKS5_AUTH(3) from curl 8.23.0-r0 (Chainguard OS)
Source: https://github.com/curl/curl.git