> ## Documentation Index
> Fetch the complete documentation index at: https://auth0.com/llms.txt
> Use this file to discover all available pages before exploring further.

> Learn about triggers, which are events that automatically invokes an Action when a specific operation, such as a user logging in, occurs at runtime.

# Explore Triggers

Triggers are points in the Auth0 process where Actions can be added for required customization. Multiple Actions can be placed in a Trigger, executing in sequence. Excluding the Custom Token Exchange, triggers can be synchronous (blocking) or asynchronous (non-blocking). Each trigger has specific Objects and APIs. They may differ based on your connection (such as <Tooltip tip="Passwordless: Form of authentication that does not rely on a password as the first factor." cta="View Glossary" href="/docs/glossary?term=passwordless">passwordless</Tooltip> connection).

To explore reference Objects and APIs for specific Actions for a trigger, select the trigger below, noting Auth0's definition of a [passwordless connection](/docs/authenticate/passwordless).

#### Signup and Login

When a user is added to a database or passwordless connection (Signup), or as part of a user's authentication transaction (Login).

| Trigger                  | Description                                                          |
| ------------------------ | -------------------------------------------------------------------- |
| `pre-user-registration`  | Triggers before a user is created.                                   |
| `post-user-registration` | Triggers asynchronously after a user is created.                     |
| `post-login`             | Triggers after a user is authenticated but before a token is issued. |

#### MFA Notifications

When using SMS as a factor for <Tooltip tip="Multi-factor authentication (MFA): User authentication process that uses a factor in addition to username and password such as a code via SMS." cta="View Glossary" href="/docs/glossary?term=Multi-Factor+Authentication">Multi-Factor Authentication</Tooltip> (MFA) or to configure a custom provider.

| Trigger              | Description                                                                                              |
| -------------------- | -------------------------------------------------------------------------------------------------------- |
| `send-phone-message` | Triggers when using a custom provider to send the messages for the enrollment and the challenge process. |

#### Password Reset

When a password reset request is initiated.

| Trigger                         | Description                                                                       |
| ------------------------------- | --------------------------------------------------------------------------------- |
| `post-change-password`          | Triggers after a password is changed.                                             |
| `password-reset-post-challenge` | Triggers after the first challenge is completed and before the password is reset. |

#### Machine to Machine

When an application, instead of a user, is authenticated and authorized to use your APIs.

| Trigger                | Description                                  |
| ---------------------- | -------------------------------------------- |
| `credentials-exchange` | Triggers before an access token is returned. |

### Custom Token Exchange

When a Custom Token Exchange Request is received to log a user in.

| Trigger                 | Description                                                                |
| ----------------------- | -------------------------------------------------------------------------- |
| `custom-token-exchange` | Triggers at first step for the transaction, before the post-login trigger. |