Plugins

Plugins are a key part of Better Auth, they let you extend the base functionalities. You can use them to add new authentication methods, features, or customize behaviors.

Better Auth offers comes with many built-in plugins ready to use. Check the plugins section for details. You can also create your own plugins.

Using a Plugin

Plugins can be a server-side plugin, a client-side plugin, or both.

To add a plugin on the server, include it in the plugins array in your auth configuration. The plugin will initialize with the provided options.

import { betterAuth } from "better-auth";
 
export const auth = betterAuth({
    plugins: [
        // Add your plugins here
    ]
});

Client plugins are added when creating the client. Most plugin require both server and client plugins to work correctly. The Better Auth auth client on the frontend uses the createAuthClient function provided by better-auth/client.

import { createAuthClient } from "better-auth/client";
 
const authClient =  createAuthClient({
    plugins: [
        // Add your client plugins here
    ]
});

We recommend keeping the auth-client and your normal auth instance in separate files.

Creating a Plugin

To get started, you'll need a server plugin. Server plugins are the backbone of all plugins, and client plugins are there to provide an interface with frontend APIs to easily work with your server plugins.

What can a plugin do?

• Create custom endpoints to perform any action you want.
• Extend database tables with custom schemas.
• Use a middleware to target a group of routes using it's route matcher, and run only when those routes are called through a request.
• Use hooks to target a specific route or request. And if you want to run the hook even if the endpoint is called directly.
• Use onRequest or onResponse if you want to do something that affects all requests or responses.
• Create custom rate-limit rule.

Create a Server plugin

To create a server plugin you need to pass an object that satisfies the BetterAuthPlugin interface.

The only required property is id, which is a unique identifier for the plugin. Both server and client plugins can use the same id.

import type { BetterAuthPlugin } from "better-auth";
 
export const myPlugin = ()=>{
    return {
        id: "my-plugin",
    } satisfies BetterAuthPlugin
}

Endpoints

To add endpoints to the server, you can pass endpoints which requires an object with the key being any string and the value being an AuthEndpoint.

To create an Auth Endpoint you'll need to import createAuthEndpoint from better-auth.

Better Auth uses wraps around another library called Better Call to create endpoints. Better call is a simple ts web framework made by the same team behind Better Auth.

import { createAuthEndpoint } from "better-auth/api";
 
const myPlugin = ()=> {
    return {
        id: "my-plugin",
        endpoints: {
            getHelloWorld: createAuthEndpoint("/my-plugin/hello-world", {
                method: "GET",
            }, async(ctx) => {
                return ctx.json({
                    message: "Hello World"
                })
            })
        }
    } satisfies BetterAuthPlugin
}

Create Auth endpoints wraps around createEndpoint from Better Call. Inside the ctx object, it'll provide another object called context that give you access better-auth specific contexts including options, db, baseURL and more.

Context Object

• appName: The name of the application. Defaults to "Better Auth".
• options: The options passed to the Better Auth instance.
• tables: Core tables definition. It is an object which has the table name as the key and the schema definition as the value.
• baseURL: the baseURL of the auth server. This includes the path. For example, if the server is running on http://localhost:3000, the baseURL will be http://localhost:3000/api/auth by default unless changed by the user.
• session: The session configuration. Includes updateAge and expiresIn values.
• secret: The secret key used for various purposes. This is defined by the user.
• authCookie: The default cookie configuration for core auth cookies.
• logger: The logger instance used by Better Auth.
• db: The Kysely instance used by Better Auth to interact with the database.
• adapter: This is the same as db but it give you orm like functions to interact with the database. (we recommend using this over db unless you need raw sql queries or for performance reasons)
• internalAdapter: These are internal db calls that are used by Better Auth. For example, you can use these calls to create a session instead of using adapter directly. internalAdapter.createSession(userId)
• createAuthCookie: This is a helper function that let's you get a cookie name and options for either to set or get cookies. It implements things like __secure prefix and __host prefix for cookies based on

For other properties, you can check the Better Call documentation and the source code .

Rules for Endpoints

• Makes sure you use kebab-case for the endpoint path
• Make sure to only use POST or GET methods for the endpoints.
• Any function that modifies a data should be a POST method.
• Any function that fetches data should be a GET method.
• Make sure to use the createAuthEndpoint function to create API endpoints.
• Make sure your paths are unique to avoid conflicts with other plugins. If you're using a common path, add the plugin name as a prefix to the path. (/my-plugin/hello-world instead of /hello-world.)

Schema

You can define a database schema for your plugin by passing a schema object. The schema object should have the table name as the key and the schema definition as the value.

import { BetterAuthPlugin } from "better-auth/plugins";
 
const myPlugin = ()=> {
    return {
        id: "my-plugin",
        schema: {
            myTable: {
                fields: {
                    name: {
                        type: "string"
                    }
                },
                modelName: "myTable" // optional if you want to use a different name than the key
            }
        }
    } satisfies BetterAuthPlugin
}

Fields

By default better-auth will create an id field for each table. You can add additional fields to the table by adding them to the fields object.

The key is the column name and the value is the column definition. The column definition can have the following properties:

type: The type of the filed. It can be string, number, boolean, date.

required: if the field should be required on a new record. (default: false)

unique: if the field should be unique. (default: false)

reference: if the field is a reference to another table. (default: null) It takes an object with the following properties:

• model: The table name to reference.
• field: The field name to reference.
• onDelete: The action to take when the referenced record is deleted. (default: null)

Other Schema Properties

disableMigration: if the table should not be migrated. (default: false)

const myPlugin = (opts: PluginOptions)=>{
    return {
        id: "my-plugin",
        schema: {
            rateLimit: {
                fields: {
                    key: {
                        type: "string",
                    },
                },
                disableMigration: opts.storage.provider !== "database", 
            },
        },
    } satisfies BetterAuthPlugin
}

if you add additional fields to a user or session table, the types will be inferred automatically on getSession and signUpEmail calls.

 
const myPlugin = ()=>{
    return {
        id: "my-plugin",
        schema: {
            user: {
                fields: {
                    age: {
                        type: "number",
                    },
                },
            },
        },
    } satisfies BetterAuthPlugin
}

This will add an age field to the user table and all user returning endpoints will include the age field and it'll be inferred properly by typescript.

Hooks

Hooks are used to run code before or after an action is performed, either from a client or directly on the server. You can add hooks to the server by passing a hooks object, which should contain before and after properties.

import {  createAuthMiddleware } from "better-auth/plugins";
 
const myPlugin = ()=>{
    return {
        id: "my-plugin",
        hooks: {
            before: [{
                    matcher: (context)=>{
                        return context.headers.get("x-my-header") === "my-value"
                    },
                    handler: createAuthMiddleware(async(ctx)=>{
                        //do something before the request
                        return  {
                            context: ctx // if you want to modify the context
                        }
                    })
                }],
            after: [{
                matcher: (context)=>{
                    return context.path === "/sign-up/email"
                },
                handler: async(ctx)=>{
                    return ctx.json({
                        message: "Hello World"
                    }) // if you want to modify the response
                }
            }]
        }
    } satisfies BetterAuthPlugin
}

Middleware

You can add middleware to the server by passing a middleware array. This array should contain middleware objects, each with a path and a middleware property. Unlike hooks, middleware only runs on api requests from a client. If the endpoint is invoked directly, the middleware will not run.

The path can be either a string or a path matcher, using the same path-matching system as better-call.

If you throw an APIError from the middleware or returned a Response object, the request will be stopped and the response will be sent to the client.

const myPlugin = ()=>{
    return {
        id: "my-plugin",
        middleware: [
            {
                path: "/my-plugin/hello-world",
                middleware: createAuthMiddleware(async(ctx)=>{
                    //do something
                })
            }
        ]
    } satisfies BetterAuthPlugin
}

On Request & On Response

Additional to middlewares, you can also hook into right before a request is made and right after a response is returned. This is mostly useful if you want to do something that affects all requests or responses.

On Request

The onRequest function is called right before the request is made. It takes two parameters: the request and the context object.

Here’s how it works:

• Continue as Normal: If you don't return anything, the request will proceed as usual.
• Interrupt the Request: To stop the request and send a response, return an object with a response property that contains a Response object.
• Modify the Request: You can also return a modified request object to change the request before it's sent.

const myPlugin = ()=> {
    return  {
        id: "my-plugin",
        onRequest: async (request, context) => {
            //do something
        },
    } satisfies BetterAuthPlugin
}

On Response

The onResponse function is executed immediately after a response is returned. It takes two parameters: the response and the context object.

Here’s how to use it:

• Modify the Response: You can return a modified response object to change the response before it is sent to the client.
• Continue Normally: If you don’t return anything, the response will be sent as is.

const myPlugin = ()=>{
    return {
        id: "my-plugin",
        onResponse: async (response, context) => {
            //do something
        },
    } satisfies BetterAuthPlugin
}

Rate Limit

You can define custom rate limit rules for your plugin by passing a rateLimit array. The rate limit array should contain an array of rate limit objects.

const myPlugin = ()=>{
    return {
        id: "my-plugin",
        rateLimit: [
            {
                pathMatcher: (path)=>{
                    return path === "/my-plugin/hello-world"
                },
                limit: 10,
                window: 60,
            }
        ]
    } satisfies BetterAuthPlugin
}

Server-plugin helper functions

Some additional helper functions for creating server plugins.

getSessionFromCtx

Allows you to get the client's session data by passing the auth middleware's context.

import {  createAuthMiddleware } from "better-auth/plugins";
 
const myPlugin = {
    id: "my-plugin",
    hooks: {
        before: [{
                matcher: (context)=>{
                    return context.headers.get("x-my-header") === "my-value"
                },
                handler: createAuthMiddleware(async (ctx) => {
                    const session = await getSessionFromCtx(ctx);
                    //do something with the client's session.
 
                    return  {
                        context: ctx
                    }
                })
            }],
    }
} satisfies BetterAuthPlugin

sessionMiddleware

A middleware that checks if the client has a valid session. If the client has a valid session, it'll add the session data to the context object.

import { createAuthMiddleware } from "better-auth/plugins";
import { sessionMiddleware } from "better-auth/api";
 
const myPlugin = ()=>{
    return {
        id: "my-plugin",
        endpoints: {
            getHelloWorld: createAuthEndpoint("/my-plugin/hello-world", {
                method: "GET",
                use: [sessionMiddleware], 
            }, async(ctx) => {
                const session = ctx.context.session;
                return ctx.json({
                    message: "Hello World"
                })
            })
        }
    } satisfies BetterAuthPlugin
}

Creating a client plugin

If your endpoints needs to be called from the client, you'll need to also create a client plugin. Better Auth clients can infer the endpoints from the server plugins. You can also add additional client side logic.

import type { BetterAuthClientPlugin } from "better-auth";
 
export const myPluginClient = ()=>{
    return {
        id: "my-plugin",
    } satisfies BetterAuthClientPlugin
}

Endpoint Interface

Endpoints are inferred from the server plugin by adding a $InferServerPlugin key to the client plugin.

The client infers the path as an object and converts kebab-case to camelCase. For example, /my-plugin/hello-world becomes myPlugin.helloWorld.

import type { BetterAuthClientPlugin } from "better-auth/client";
import type { myPlugin } from "./plugin";
 
const myPluginClient = ()=> {
    return  {
        id: "my-plugin",
        $InferServerPlugin: {} as ReturnType<typeof myPlugin>,
    } satisfies BetterAuthClientPlugin
}

Get actions

If you need to add additional methods or what not to the client you can use the getActions function. This function is called with the fetch function from the client.

Better Auth uses Better fetch to make requests. Better fetch is a simple fetch wrapper made by the same author of Better Auth.

import type { BetterAuthClientPlugin } from "better-auth/client";
import type { myPlugin } from "./plugin";
import type { BetterFetchOption } from "@better-fetch/fetch";
 
const myPluginClient = {
    id: "my-plugin",
    $InferServerPlugin: {} as ReturnType<typeof myPlugin>,
    getActions: ($fetch)=>{
        return {
            myCustomAction: async (data: {
                foo: string,
            }, fetchOptions?: BetterFetchOption)=>{
                const res = $fetch("/custom/action", {
                    method: "POST",
                    body: {
                        foo: data.foo
                    },
                    ...fetchOptions
                })
                return res
            }
        }
    }
} satisfies BetterAuthClientPlugin

Get Atoms

This is only useful if you want to provide hooks like useSession.

Get atoms is called with the fetch function from better fetch and it should return an object with the atoms. The atoms should be created using nanostores. The atoms will be resolved by each framework useStore hook provided by nanostores.

import { atom } from "nanostores";
import type { BetterAuthClientPlugin } from "better-auth/client";
 
const myPluginClient = {
    id: "my-plugin",
    $InferServerPlugin: {} as ReturnType<typeof myPlugin>,
    getAtoms: ($fetch)=>{
        const myAtom = atom<null>()
        return {
            myAtom
        }
    }
} satisfies BetterAuthClientPlugin

See built in plugins for examples of how to use atoms properly.

Path methods

by default, inferred paths use GET method if they don't require a body and POST if they do. You can override this by passing a pathMethods object. The key should be the path and the value should be the method ("POST" | "GET").

import type { BetterAuthClientPlugin } from "better-auth/client";
import type { myPlugin } from "./plugin";
 
const myPluginClient = {
    id: "my-plugin",
    $InferServerPlugin: {} as ReturnType<typeof myPlugin>,
    pathMethods: {
        "/my-plugin/hello-world": "POST"
    }
} satisfies BetterAuthClientPlugin

Fetch plugins

If you need to use better fetch plugins you can pass them to the fetchPlugins array. You can read more about better fetch plugins in the better fetch documentation.

Atom Listeners

This is only useful if you want to provide hooks like useSession and you want to listen to atoms and re-evaluate them when they change.

You can see how this is used in the built-in plugins.