Changelog

4.57.1

(fix): Only copy custom_pagination.py into generated SDKs when custom pagination endpoints are present, and only copy pagination.py when standard pagination endpoints are present.

4.57.0

(feat): Add custom_transport: true generator config option that exposes an http_client parameter on generated client constructors for custom httpx transport injection.

Primary use case: Enables PKCE (Proof Key for Code Exchange) OAuth flows and other authentication schemes that require request interception at the transport layer.

Configuration:

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generators:
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  - name: fernapi/fern-python-sdk
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    config:
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      custom_transport: true

Generated parameter types:

• Sync client: http_client: typing.Optional[httpx.BaseTransport]
• Async client: http_client: typing.Optional[httpx.AsyncBaseTransport]

Use cases:

• PKCE OAuth authentication flows requiring code challenge/verifier injection
• Custom request signing or authentication header manipulation
• Request/response interception and modification
• Mock transports for testing without network calls
• Custom retry logic beyond the built-in exponential backoff

Example pattern (Twilio SDK style):

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# SDK developer provides a factory method in custom code
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class ValidationClient:
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    @classmethod
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    def create(cls, account_sid: str, auth_token: str) -> httpx.BaseTransport:
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        # Custom transport with PKCE or validation logic
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        return CustomValidationTransport(account_sid, auth_token)
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# End-user usage
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from myapi import MyClient, ValidationClient
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validation_transport = ValidationClient.create("account_sid", "auth_token")
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client = MyClient(http_client=validation_transport, base_url="https://api.example.com")

This feature allows SDK developers to defer transport-specific logic to custom code while the generator simply threads the transport through to httpx.Client/httpx.AsyncClient.