auth error code and some unit tests

[Rader]

What is this feature?

two major changes:

• repo's LastCommit and Tree api use 403 error instead of 401 if user has no permission to access the repo
• some unit test for user, sensitive checking related

Why do we need this feature?

• auth code 403 tell the client to show error message instead of ask user to login
• unit test for better code quality

Who is this feature for?

N/A

Which issue(s) does this PR fix?:

N/A

Special notes for your reviewer:

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[starship-github]

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