---
name: "CURLOPT_SOCKS5_AUTH"
section: "3"
platform: "linux"
package: "curl"
version: "8.23.0-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "macos"]
url: "https://new.carta.tech/CURLOPT_SOCKS5_AUTH"
---

# CURLOPT\_SOCKS5\_AUTH(3)

methods for SOCKS5 proxy authentication

## NAME

CURLOPT\_SOCKS5\_AUTH - methods for SOCKS5 proxy authentication

## SYNOPSIS

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

## 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)](/CURLOPT_PROXYUSERPWD/3.md)* 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)](/curl_easy_setopt/3.md)* 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

CURLAUTH\_BASIC \| CURLAUTH\_GSSAPI

## PROTOCOLS

This functionality affects all supported protocols

## 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

**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)](/curl_easy_setopt/3.md)*.

*CURLAUTH\_ONLY* is supported since 8.23.0.

## AVAILABILITY

Added in curl 7.55.0

## RETURN VALUE

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

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

## SEE ALSO

[**CURLOPT\_PROXY**(3)](/CURLOPT_PROXY/3.md), [**CURLOPT\_PROXYTYPE**(3)](/CURLOPT_PROXYTYPE/3.md)