Implement Unit Tests for Auth Service

[tryyang2001]

Pull Request

Description

• added unit tests for each auth endpoints
• improve github workflow to test across different node versions

Related Issue(s)

Closes #129 The README will be completed by @tlyi .

Changes Made

Screenshots (if applicable)

Checklist

• [x] I have checked that the changes included in the PR are intended to merge to master or any destination branch.
• [x] I have verified that the new changes do not break any existing functionalities, unless the new changes are intended and have approved by the team.
• [x] I will take care of the merging and delete the side-branch after the PR is merged.

Additional Notes/References

Merged this only after this PR