---
name: "nng_tls_config_auth_mode"
section: "3tls"
platform: "linux"
package: "libnng-dev"
version: "1.10.1-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/nng_tls_config_auth_mode"
---

# nng\_tls\_config\_auth\_mode(3tls)

configure authentication mode

## NAME

nng\_tls\_config\_auth\_mode - configure authentication mode

## SYNOPSIS

```
#include <nng/nng.h>
#include <nng/supplemental/tls/tls.h>
typedef enum nng_tls_auth_mode {
        NNG_TLS_AUTH_MODE_NONE,
        NNG_TLS_AUTH_MODE_OPTIONAL,
        NNG_TLS_AUTH_MODE_REQUIRED
} nng_tls_auth_mode;
int nng_tls_config_auth_mode(nng_tls_config *cfg, nng_tls_auth_mode mode);
```

## DESCRIPTION

The `nng_tls_config_auth_mode()` function configures the authentication mode to be used for TLS sessions using this configuration object.

The possible modes are:

`NNG_TLS_AUTH_MODE_NONE`

No authentication of the TLS peer is performed. This is the default for TLS servers, which most typically do not authenticate their clients.

`NNG_TLS_AUTH_MODE_OPTIONAL`

If a certificate is presented by the peer, then it is validated. However, if the peer does not present a valid certificate, then the session is allowed to proceed without authentication.

`NNG_TLS_AUTH_MODE_REQUIRED`

A check is made to ensure that the peer has presented a valid certificate used for the session. If the peer’s certificate is invalid or missing, then the session is refused. This is the default for clients.

## RETURN VALUES

This function returns 0 on success, and non-zero otherwise.

## ERRORS

`NNG_ENOMEM`

Insufficient memory is available.

`NNG_EINVAL`

An invalid *mode* was specified.

`NNG_EBUSY`

The configuration *cfg* is already in use, and cannot be modified.

## SEE ALSO

[nng\_strerror(3)](/nng_strerror/3.md), [nng\_tls\_config\_alloc(3tls)](/nng_tls_config_alloc/3tls.md), [nng\_tls\_config\_ca\_chain(3tls)](/nng_tls_config_ca_chain/3tls.md), [nng\_tls\_config\_ca\_file(3tls)](/nng_tls_config_ca_file/3tls.md), [nng\_tls\_config\_server\_name(3tls)](/nng_tls_config_server_name/3tls.md), [nng(7)](/nng/7.md)