Authentication

Model auth schemes such as bearer, basic, custom headers, and oauth.

Configuring authentication schemes happens in the api.yml file.

$fern/
>├─ fern.config.json # root-level configuration
>├─ generators.yml # generators you're using
>└─ definition/
>  ├─ api.yml  # API-level configuration
>  └─ imdb.yml # endpoints, types, and errors

To add an authentication scheme, specify the authentication method under the auth-schemes section.

1auth-schemes:
2  AuthScheme:                     
3    ...

To apply an authentication scheme across all endpoints, reference the auth-scheme within the auth section of your api.yml file.

1auth: AuthScheme                  
2auth-schemes:
3  AuthScheme:                     
4    ...

Bearer authentication

Start by defining a Bearer authentication scheme in api.yml:

api.yml
1auth: Bearer                  
2auth-schemes:
3  Bearer:                     
4    scheme: bearer

This will generate an SDK where the user would have to provide a mandatory argument called token.

index.ts
1const client = new Client({
2  token: "ey34..."
3})

If you want to control variable naming and the environment variable to scan, use the configuration below:

api.yml
1auth: Bearer                  
2auth-schemes:
3  Bearer:                     
4    scheme: bearer
5    token:
6      name: apiKey 
7      env: PLANTSTORE_API_KEY

The generated SDK would look like:

index.ts
1// Uses process.env.PLANTSTORE_API_KEY
2let client = new Client(); 
3
4// token has been renamed to apiKey
5client = new Client({
6  apiKey: "ey34..."
7})

Basic authentication

Start by defining a Basic authentication scheme in api.yml:

api.yml
1auth: Basic                  
2auth-schemes:
3  Basic:                     
4    scheme: basic

This will generate an SDK where the user would have to provide a mandatory arguments called username and password.

index.ts
1const client = new Client({
2  username: "joeschmoe"
3  password: "ey34..."
4})

If you want to control variable naming and environment variables to scan, use the configuration below:

api.yml
1auth: Basic                  
2auth-schemes:
3  Basic:                     
4    scheme: basic
5    username:
6      name: clientId
7      env: PLANTSTORE_CLIENT_ID
8    password:
9      name: clientSecret
10      env: PLANTSTORE_CLIENT_SECRET

The generated SDK would look like:

index.ts
1// Uses process.env.PLANTSTORE_CLIENT_ID and process.env.PLANTSTORE_CLIENT_SECRET
2let client = new Client(); 
3
4// parameters have been renamed
5client = new Client({
6  clientId: "joeschmoe", 
7  clientSecret: "ey34..."
8})

Custom header (e.g. API key)

You can also create your own authentication scheme with customized headers.

api.yml
1auth: ApiKeyAuthScheme
2auth-schemes:
3  ApiKeyAuthScheme:
4    header: X-API-Key
5    type: string

This will generate an SDK where the user would have to provide a mandatory argument called apiKey.

index.ts
1const client = new Client({
2  xApiKey: "ey34..."
3})

If you want to control variable naming and environment variables to scan, use the configuration below:

api.yml
1auth: ApiKeyAuthScheme
2auth-schemes:
3  ApiKeyAuthScheme:
4    header: X-API-Key
5    type: string
6    name: apiKey
7    env: PLANTSTORE_API_KEY

The generated SDK would look like:

index.ts
1// Uses process.env.PLANTSTORE_API_KEY
2let client = new Client(); 
3
4// parameters have been renamed
5client = new Client({
6  apiKey: "ey34..."
7})

OAuth client credentials

If your API uses OAuth, you can specify an oauth scheme. Note that you’ll need to define a token retrieval endpoint.

api.yml
1name: api
2
3imports:
4  auth: auth.yml
5
6auth: OAuthScheme
7auth-schemes:
8  OAuthScheme:
9    scheme: oauth
10    type: client-credentials
11    client-id-env: YOUR_CLIENT_ID
12    client-secret-env: YOUR_CLIENT_SECRET
13    get-token:
14      endpoint: auth.getToken               
15      response-properties:
16        access-token: $response.access_token 
17        expires-in: $response.expires_in

If the expires-in property is set, the generated OAuth token provider will automatically refresh the token when it expires. Otherwise, it’s assumed that the access token is valid indefinitely.

With this, all of the OAuth logic happens automatically in the generated SDKs. As long as you configure these settings, your client will automatically retrieve an access token and refresh it as needed.