feat: expose externalToken on AuthenticationResponse

[itaihanski]

Related Issues

https://github.com/descope/etc/issues/16830

Related PRs

descope/descope-kotlin#336
descope/descope-js#1435

Description

• Populate AuthenticationResponse.externalToken: String? from the server auth response
• Decoded on JWTResponse and passed through convert(), matching the Flutter and web SDKs

Must

• Tests
• Documentation

[shuni-bot]

🐕 Review complete — View session on Shuni Portal 🐾

[shuni-bot]

🐕 Suggested Reviewers

The review assignment focuses on contributors with comprehensive coverage of the affected files and core familiarity with the codebase to ensure a broad and effective review.

Reviewer	Reason
shilgapira	Shilgapira has extensive commit history across multiple files involved in this change, including HTTP handling, routes, and response types, making them well-suited to review both the functional and integration aspects.

_{Suggested by Shuni based on git history and PR context. Names are not @-mentioned to avoid notifying anyone — request a review from whoever fits best.}

[shuni-bot]

🐕 Shuni's Review

Threads externalToken from the server JWT response through JWTResponse.convert() onto the public AuthenticationResponse, matching the Flutter/web SDKs.

No issues found — good bones! 🦴

Decoding is auto-synthesized, the flow auth path carries it through, the other init call sites (migrate / provided-session) correctly default to nil, and both present/absent cases are tested. Woof!