@ory/client-fetch: toSession() overwrites Cookie header when using initOverrides.headers

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Ory Network Project

No response

Describe the bug

When using @ory/client-fetch, the toSession() method allows passing a cookie parameter as part of requestParameters, which correctly sets the Cookie header — unless initOverrides.headers is also provided. In that case, the SDK silently overwrites the Cookie header with the contents of initOverrides.headers, leading to unexpected 401 Unauthorized response.

Reproducing the bug

const session = await api.toSession(
  { cookie },
  {
    headers: {
      'Cache-Control': 'max-age=0'
    }
  }
);

Expected behavior:
The request sends both Cookie and Cache-Control headers

Actual behavior:
Only Cache-Control is sent. Cookie is silently overwritten. Request fails with 401 Unauthorized.

Workaround

Manually add the cookie into headers:

const session = await api.toSession(
  { cookie },
  {
    headers: {
      'Cache-Control': 'max-age=0',
      'Cookie': cookie
    }
  }
);

Relevant log output

Relevant configuration

Version

"@ory/client-fetch": "1.22.4"

On which operating system are you observing this issue?

None

In which environment are you deploying?

None

Additional Context

No response

Start in the generated @ory/client-fetch implementation of toSession(), focusing on how requestParameters.cookie and initOverrides.headers are combined. Reproduce the example with both headers, then verify the fix preserves Cookie alongside Cache-Control and prevents the resulting 401 response.