# Passport Strategy Adapter

_Important: We strongly recommend that users learn LoopBack's
[authentication system](https://loopback.io/doc/en/lb4/Authentication-overview.html)
before using this module._

LoopBack 4 authentication system is highly extensible and give users the
flexibility to provide custom strategies. To be compatible with over 500+
Express [`passport`](https://www.npmjs.com/package/passport) middleware, this
adapter module is created for plugging in
[`passport`](https://www.npmjs.com/package/passport) based strategies to the
authentication system in `@loopback/authentication@3.x`.

If you would like to try with an example,
[`@loopback/example-passport-login`](https://github.com/strongloop/loopback-next/tree/master/examples/passport-login)
uses this module to authenticate APIs with several OAuth 2.0 passport strategies
like Facebook, Google.

## Installation

```sh
npm i @loopback/authentication-passport --save
```

## Background

`@loopback/authentication@3.x` allows users to register authentication
strategies that implement the interface
[`AuthenticationStrategy`](https://loopback.io/doc/en/lb4/apidocs.authentication.authenticationstrategy.html)

Since `AuthenticationStrategy` describes a strategy with different contracts
than the passport
[`Strategy`](https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/types/passport/index.d.ts#L79),
and we'd like to support the existing 500+ community passport strategies, an
**adapter class** is created in this package to convert a passport strategy to
the one that LoopBack 4 authentication system wants.

## Usage

For the examples that follow, we will be using `passport-http`, so be sure to
install these modules:

```
npm i passport-http @types/passport-http --save
```

### Simple Usage

1. Create an instance of the passport strategy

   Taking the basic strategy exported from
   [`passport-http`](https://github.com/jaredhanson/passport-http) as an
   example, first create an instance of the basic strategy with your `verify`
   function.

   ```ts
   // Create a file named `my-basic-auth-strategy.ts` to define your strategy below

   import {BasicStrategy} from 'passport-http';

   function verify(username: string, password: string, cb: Function) {
     users.find(username, password, cb);
   }
   const basicStrategy = new BasicStrategy(verify);
   ```

   It's a similar configuration as you add a strategy to a `passport` by calling
   `passport.use()`.

2. Supply a _user profile factory_ which converts a user to a user profile. It
   must abide by the `UserProfileFactory` interface supplied by
   `@loopback/authentication@3.x`.

   It is shown below for your convenience.

   ```ts
   export interface UserProfileFactory<U> {
     (user: U): UserProfile;
   }
   ```

   A default user profile factory is provided for you in the StrategyAdapter
   constructor, but it does very little. It simply returns the user model as-is.

   ```ts
   private userProfileFactory: UserProfileFactory<U> = (u: unknown) => {
         return u as UserProfile;
   },
   ```

   So it is recommended you provide a more meaningful mapping.

   An example of a user profile factory converting a specific user type `MyUser`
   to type `UserProfile` is shown below.

   ```ts
   //In file 'my.userprofile.factory.ts'

   import {UserProfileFactory} from '@loopback/authentication';
   import {securityId, UserProfile} from '@loopback/security';

   export const myUserProfileFactory: UserProfileFactory<MyUser> = function (
     user: MyUser,
   ): UserProfile {
     const userProfile = {[securityId]: user.id};
     return userProfile;
   };
   ```

3. Apply the adapter to the strategy

   ```ts
   // In file 'my-basic-auth-strategy.ts'
   import {BasicStrategy} from 'passport-http';
   import {UserProfileFactory} from '@loopback/authentication';
   import {securityId, UserProfile} from '@loopback/security';
   import {myUserProfileFactory} from '<path to user profile factory>';

   function verify(username: string, password: string, cb: Function) {
     users.find(username, password, cb);
   }
   const basicStrategy = new BasicStrategy(verify);

   // Apply the adapter
   export const AUTH_STRATEGY_NAME = 'basic';
   export const basicAuthStrategy = new StrategyAdapter(
     // The configured basic strategy instance
     basicStrategy,
     // Give the strategy a name
     // You'd better define your strategy name as a constant, like
     // `const AUTH_STRATEGY_NAME = 'basic'`.
     // You will need to decorate the APIs later with the same name.
     AUTH_STRATEGY_NAME,
     // Provide a user profile factory
     myUserProfileFactory,
   );
   ```

4. Register(bind) the strategy to app

   ```ts
   import {Application, CoreTags} from '@loopback/core';
   import {AuthenticationBindings} from '@loopback/authentication';
   import {basicAuthStrategy} from './my-basic-auth-strategy';

   app
     .bind('authentication.strategies.basicAuthStrategy')
     .to(basicAuthStrategy)
     .tag({
       [CoreTags.EXTENSION_FOR]:
         AuthenticationBindings.AUTHENTICATION_STRATEGY_EXTENSION_POINT_NAME,
     });
   ```

5. Decorate your endpoint

   To authenticate your request with the basic strategy, decorate your
   controller function like:

   ```ts
   import {AUTH_STRATEGY_NAME} from './my-basic-auth-strategy';
   import {SecurityBindings, UserProfile} from '@loopback/security';
   import {authenticate} from '@loopback/authentication';

   class MyController {
     constructor(
       @inject(SecurityBindings.USER, {optional: true})
       private user: UserProfile,
     ) {}

     // Define your strategy name as a constant so that
     // it is consistent with the name you provide in the adapter
     @authenticate(AUTH_STRATEGY_NAME)
     async whoAmI(): Promise<string> {
       return this.user.id;
     }
   }
   ```

6. Add the authentication action to your sequence

   This part is same as registering a non-passport based strategy. Please make
   sure you follow the documentation
   [adding-an-authentication-action-to-a-custom-sequence](https://loopback.io/doc/en/lb4/Loopback-component-authentication.html#adding-an-authentication-action-to-a-custom-sequence)
   to rewrite your sequence. You can also find a sample implementation in
   [this example tutorial](https://loopback.io/doc/en/lb4/Authentication-tutorial.html#creating-a-custom-sequence-and-adding-the-authentication-action).

### With Provider

If you need to inject stuff (e.g. the verify function, user profile factory
function) when configuring the strategy, you may want to provide your strategy
as a provider.

_Note: If you are not familiar with LoopBack providers, check the documentation
in
[Extending LoopBack 4](https://loopback.io/doc/en/lb4/Extending-LoopBack-4.html)_

1. Create a provider for the strategy

   Use `passport-http` as the example again:

   ```ts
   // Create a file named `my-basic-auth-strategy.ts` to define your strategy below

   import {AuthenticationStrategy} from '@loopback/authentication';
   import {Provider} from '@loopback/core';

   class PassportBasicAuthProvider implements Provider<AuthenticationStrategy> {
     value(): AuthenticationStrategy {
       // The code that returns the converted strategy
     }
   }
   ```

   The Provider should have two functions:

   - A function that takes in the verify callback function and returns a
     configured basic strategy. To know more about the configuration, please
     check
     [the configuration guide in module `passport-http`](https://github.com/jaredhanson/passport-http#usage-of-http-basic).

   - A function that applies the `StrategyAdapter` to the configured basic
     strategy instance. Then in the `value()` function, you return the converted
     strategy.

   So a full implementation of the provider is:

   ```ts
   // In file 'providers/my-basic-auth-strategy.ts'

   import {BasicStrategy, BasicVerifyFunction} from 'passport-http';
   import {StrategyAdapter} from `@loopback/passport-adapter`;
   import {
     AuthenticationStrategy,
     AuthenticationBindings,
   } from '@loopback/authentication';
   import {Provider, inject} from '@loopback/core';

   export class PassportBasicAuthProvider<MyUser>
     implements Provider<AuthenticationStrategy> {
     constructor(
       @inject('authentication.basic.verify')
       private verifyFn: BasicVerifyFunction,
       @inject(AuthenticationBindings.USER_PROFILE_FACTORY)
       private myUserProfileFactory: UserProfileFactory<MyUser>,
     ) {}

     value(): AuthenticationStrategy {
       const basicStrategy = this.configuredBasicStrategy(this.verifyFn);
       return this.convertToAuthStrategy(basicStrategy);
     }

     // Takes in the verify callback function and returns a configured basic strategy.
     configuredBasicStrategy(verifyFn: BasicVerifyFunction): BasicStrategy {
       return new BasicStrategy(verifyFn);
     }

     // Applies the `StrategyAdapter` to the configured basic strategy instance.
     // You'd better define your strategy name as a constant, like
     // `const AUTH_STRATEGY_NAME = 'basic'`
     // You will need to decorate the APIs later with the same name
     // Pass in the user profile factory
     convertToAuthStrategy(basic: BasicStrategy): AuthenticationStrategy {
       return new StrategyAdapter(
         basic,
         AUTH_STRATEGY_NAME,
         this.myUserProfileFactory,
       );
     }
   }
   ```

2. Create a provider for the verify function.

   Here is an example provider named VerifyFunctionProvider which has a
   `value()` method that returns a function of type BasicVerifyFunction.

   ```ts
   // In file 'providers/verifyfn.provider.ts'

   import {Provider} from '@loopback/core';
   import {repository} from '@loopback/repository';
   import {BasicVerifyFunction} from 'passport-http';
   import {INVALID_USER_CREDENTIALS_MESSAGE} from '../keys';

   export class VerifyFunctionProvider
     implements Provider<BasicVerifyFunction> {
     constructor(@repository('users') private userRepo: MyUserRepository) {}

     value(): BasicVerifyFunction {
       const myThis = this;

       return async function (
         username: string,
         password: string,
         cb: Function,
       ) {
         let user: MyUser;

         try {
           //find user with specific username
           const users: MyUser[] = await myThis.userRepo.find({
             where: {username: username},
           });

           // if no user found with this username, throw an error.
           if (users.length < 1) {
             let error = new Error(INVALID_USER_CREDENTIALS_MESSAGE); //assign 401 in sequence
             throw error;
           }

           //verify given password matches the user's password
           user = users[0];
           if (user.password !== password) {
             let error = new Error(INVALID_USER_CREDENTIALS_MESSAGE); //assign 401 in sequence
             throw error;
           }

           //return null for error, and the valid user
           cb(null, user);
         } catch (error) {
           //return the error, and null for the user
           cb(error, null);
         }
       };
     }
   }
   ```

3. Register(bind) the providers

   Register **VerifyFunctionProvider** which is required by
   **PassportBasicAuthProvider**. Then register **PassportBasicAuthProvider** in
   your LoopBack application so that the authentication system can look for your
   strategy by name and invoke it.

   ```ts
   // In the main file

   import {addExtension} from '@loopback/core';
   import {MyApplication} from '<path_to_your_app>';
   import {PassportBasicAuthProvider} from '<path_to_the_provider>';
   import {VerifyFunctionProvider} from '<path_to_the_provider>';
   import {
     AuthenticationBindings,
     AuthenticationComponent,
   } from '@loopback/authentication';

   const app = new MyApplication();

   //load the authentication component
   app.component(AuthenticationComponent);

   // bind the user repo
   app.bind('repositories.users').toClass(MyUserRepository);

   // bind the authenticated sequence (mentioned later in this document)
   app.sequence(MyAuthenticationSequence);

   // the verify function for passport-http
   app.bind('authentication.basic.verify').toProvider(VerifyFunctionProvider);

   // register PassportBasicAuthProvider as a custom authentication strategy
   addExtension(
     app,
     AuthenticationBindings.AUTHENTICATION_STRATEGY_EXTENSION_POINT_NAME,
     PassportBasicAuthProvider,
     {
       namespace:
         AuthenticationBindings.AUTHENTICATION_STRATEGY_EXTENSION_POINT_NAME,
     },
   );
   ```

4. Decorate your endpoint

   To authenticate your request with the basic strategy, decorate your
   controller function like:

   ```ts
   import {AUTH_STRATEGY_NAME} from './my-basic-auth-strategy';
   import {authenticate} from '@loopback/authentication';

   class MyController {
     constructor(@inject(SecurityBindings.USER) private user: UserProfile) {}

     // Define your strategy name as a constant so that
     // it is consistent with the name you provide in the adapter
     @authenticate(AUTH_STRATEGY_NAME)
     async whoAmI(): Promise<string> {
       return this.user.id;
     }
   }
   ```

5. Add the authentication action to your sequence

   This part is same as registering a non-passport based strategy. Please make
   sure you follow the documentation
   [adding-an-authentication-action-to-a-custom-sequence](https://loopback.io/doc/en/lb4/Loopback-component-authentication.html#adding-an-authentication-action-to-a-custom-sequence)
   to rewrite your sequence. You can also find a sample implementation in
   [this example tutorial](https://loopback.io/doc/en/lb4/Authentication-tutorial.html#creating-a-custom-sequence-and-adding-the-authentication-action).