3.5. Authentication token management
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## 3.5. Authentication token management

### 3.5.1. Service function to alter authentication token

    #include <security/pam_modules.h>

`int pam_sm_chauthtok(` | pamh, |
| flags, |
| argc, |
| argv`)`; |

`pam_handle_t *pamh`;
`int flags`;
`int argc`;
`const char **argv`;

#### 3.5.1.1. DESCRIPTION

The `pam_sm_chauthtok` function is the service module's implementation of the pam_chauthtok(3) interface.

This function is used to (re-)set the authentication token of the user.

Valid flags, which may be logically OR'd with PAM_SILENT, are:

PAM_SILENT

  Do not emit any messages.

PAM_CHANGE_EXPIRED_AUTHTOK

  This argument indicates to the module that the user's authentication token (password) should only be changed if it has expired. This flag is optional and must be combined with one of the following two flags. Note, however, the following two options are mutually exclusive.

PAM_PRELIM_CHECK

  This indicates that the modules are being probed as to their ready status for altering the user's authentication token. If the module requires access to another system over some network it should attempt to verify it can connect to this system on receiving this flag. If a module cannot establish it is ready to update the user's authentication token it should return PAM_TRY_AGAIN, this information will be passed back to the application.

  If the control value sufficient is used in the password stack, the PAM_PRELIM_CHECK section of the modules following that control value is not always executed.

PAM_UPDATE_AUTHTOK

  This informs the module that this is the call it should change the authorization tokens. If the flag is logically OR'd with PAM_CHANGE_EXPIRED_AUTHTOK, the token is only changed if it has actually expired.

The PAM library calls this function twice in succession. The first time with PAM_PRELIM_CHECK and then, if the module does not return PAM_TRY_AGAIN, subsequently with PAM_UPDATE_AUTHTOK. It is only on the second call that the authorization token is (possibly) changed.

#### 3.5.1.2. RETURN VALUES

PAM_AUTHTOK_ERR

  The module was unable to obtain the new authentication token.

PAM_AUTHTOK_RECOVERY_ERR

  The module was unable to obtain the old authentication token.

PAM_AUTHTOK_LOCK_BUSY

  Cannot change the authentication token since it is currently locked.

PAM_AUTHTOK_DISABLE_AGING

  Authentication token aging has been disabled.

PAM_PERM_DENIED

  Permission denied.

PAM_TRY_AGAIN

  Preliminary check was unsuccessful. Signals an immediate return to the application is desired.

PAM_SUCCESS

  The authentication token was successfully updated.

PAM_USER_UNKNOWN

  User unknown to password service.

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