[Refactor] /login route

[yuneng-jiang]

[Refactor] /login route

Relevant issues

This PR refactors the /login route's logic to another file, aiming to reuse most of this logic for a v2/login. More information about v2/login in a subsequent PR. This PR should not change the behavior of the currently login.

Tested by logging in with these credentials:

1. Default Proxy Admin (admin + master key)
2. Other Proxy Admin
3. Team Admin
4. Internal User
5. Internal Viewer
6. Bad Credentials

All verified the behavior is the same as before

Pre-Submission checklist

Please complete all items before asking a LiteLLM maintainer to review your PR

• I have Added testing in the tests/litellm/ directory, Adding at least 1 test is a hard requirement - see details
• I have added a screenshot of my new test passing locally
• My PR passes all unit tests on make test-unit
• My PR's scope is as isolated as possible, it only solves 1 specific problem

Type

🧹 Refactoring
✅ Test

Changes

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Project	Deployment	Preview	Comments	Updated (UTC)
litellm	Ready	Preview	Comment	Dec 3, 2025 7:02pm