# Application Authentication Tokens

Leverage Application specific authentication tokens to speed up certain authentication tasks.

> For the index of this section of the site, see [llms.txt](https://fusionauth.io/docs/llms.txt)

In most cases, Users authenticate using a login Id (email or username) plus a password. FusionAuth hashes passwords with a strong cryptographic hash such as BCrypt. The process of hashing is intentionally slow by design to limit the risk of brute force attacks. In some cases, you might need a way to speed up authentication without reducing the hashing strength for the normal login process.

To solve this problem, FusionAuth supports the concept of Authentication Tokens. Authentication Tokens are an Application specific way of authenticating Users. For each Application, you can enable Authentication Tokens and then allow Users to authenticate using this authentication token.

An Authentication Token is a sequence of characters and it can be used in place of your normal password. If you allow FusionAuth to generate the token for you which is highly recommended, the token is built using a secure random generator and the URL safe Base64 encoded to produce a string 43 characters in length.

While 128 bites of entropy is generally considered to be sufficiently secure , the generated Authentication Token provides 256 bites of entropy. This value is calculated by multiplying the number of characters by the entropy per character, and because a Base64 encoded character provides a entropy of 5.954 bits, a 43 character string will have 256 bits of entropy.

## Enabling Authentication Tokens

To enable Authentication Tokens, open the FusionAuth web interface and navigate to Applications from the main menu. Edit the Application you want to use Authentication Tokens for and click the Security tab. You'll see an option like this:

![Authentication Tokens](https://fusionauth.io/img/docs/screenshots/authenticate-application-security-authentication-tokens.png)

Enable this option and save the change to your Application.

## Generating Authentication Tokens

Once the Authentication Tokens are enabled for a specific Application, you can ask FusionAuth to generate one for a User by creating or updating a User Registration. To accomplish this, you will set the request parameter named `generateAuthenticationToken` to true in the request JSON like this:

`PUT /api/user/registration`

Example Request JSON

```json
{
  "generateAuthenticationToken": true,
  "registration": {
    "applicationId": "10000000-0000-0002-0000-000000000001",
    "data": {
      "displayName": "Johnny",
      "favoriteSports": [
        "Football",
        "Basketball"
      ]
    },
    "id": "00000000-0000-0002-0000-000000000000",
    "preferredLanguages": [
      "en",
      "fr"
    ],
    "roles": [
      "user",
      "community_helper"
    ],
    "timezone": "America/Chicago",
    "username": "johnny123"
  }
}
```

This request will result in a response that includes an Authentication Token like this:

Example Response JSON

```json
{
  "registration": {
    "applicationId": "10000000-0000-0002-0000-000000000001",
    "authenticationToken": "zLnHXeHRwukZuye22DRChqhxWNnlmOOD0POSC4nvm74",
    "data": {
      "displayName": "Johnny",
      "favoriteSports": [
        "Football",
        "Basketball"
      ]
    },
    "id": "00000000-0000-0002-0000-000000000000",
    "insertInstant": 1446064706250,
    "lastLoginInstant": 1456064601291,
    "preferredLanguages": [
      "en",
      "fr"
    ],
    "roles": [
      "user",
      "community_helper"
    ],
    "timezone": "America/Chicago",
    "username": "johnny123",
    "usernameStatus": "ACTIVE",
    "verified": true,
    "verifiedInstant": 1698772159415
  }
}
```

For more information, review the [User Registration APIs](https://fusionauth.io/docs/apis/registrations.md).

## Authenticating Using a Token

Once a User has been given an Application specific Authentication Token, you can supply it on the [Login API](https://fusionauth.io/docs/apis/login.md) as long as you include the Application Id in the request as well.

Note that you must provide a valid API key unless you've also unchecked the **Require an API key** setting in the Login API Settings .

Here is an example request to the Login API:

Example Request JSON

```json
{
  "loginId": "example@fusionauth.io",
  "password": "52h3h9fsjOn2Eh0+NBT3Kf6NcWFHbJ7oPD0sFsHMQps=",
  "applicationId": "10000000-0000-0002-0000-000000000001",
  "ipAddress": "192.168.1.42"
}
```
---

## Other pages in Authentication

> For the full index of this section, see [Authentication](https://fusionauth.io/docs/llms-authentication.txt).

- [Authentication Types](https://fusionauth.io/docs/authentication/authentication-types.md): Learn about the supported types of authentication.
- [Login Page Cookies](https://fusionauth.io/docs/authentication/cookies.md): Learn about the cookies set by FusionAuth.
- [Add an Identity Provider (IdP)](https://fusionauth.io/docs/authentication/identity-providers.md): Learn how to let users log in through an external identity provider such as Google or Okta.
- [Build a Login Page with the Login API](https://fusionauth.io/docs/authentication/login-api.md): Learn about the Login API and when you would use it.
- [Multi-Factor Authentication (MFA)](https://fusionauth.io/docs/authentication/multi-factor-authentication.md): Learn about how to use multi-factor authentication (MFA) in FusionAuth as a developer.
- [OAuth](https://fusionauth.io/docs/authentication/oauth.md): Learn about the OAuth 2.0 and OpenID Connect grants FusionAuth supports for login and single sign-on.
- [One-Time Passwords](https://fusionauth.io/docs/authentication/one-time-passwords.md): Create a passwordless experience using magic links and one-time passwords.
- [Passkeys](https://fusionauth.io/docs/authentication/passkeys.md): Learn about passkeys, which let users log in with a device instead of a password.