Fix Vault token auth bug

[hiyosi]

Signed-off-by: Tomoya Usami tousami@zlab.co.jp

Pull Request check list

• Commit conforms to CONTRIBUTING.md?
• Proper tests/regressions included?
• Documentation updated?

Affected functionality

UpstreamAuthority 'vault' plugin

Description of change

The Vault token will be set correctly in the Token Auth Method.

In v0.12.0, we get an error as below even if the token is given via plugin config or environment variable.

level=error msg="Fatal run error" error="rpc error: code = Unknown desc = failed to prepare authenticated client: token lookup failed: Error making API request.\n\nURL: GET http://<vault_addr>/v1/auth/token/lookup-self\nCode: 400. Errors:\n\n* missing client token"

Which issue this PR fixes

No Issues or PRs.
https://spiffe.slack.com/archives/CBNCC2V17/p1613059475073700

[amartinezfayo]

Thank you @hiyosi for this fix and the patience for the review!
I have a small comment about the test. Looking great otherwise.

[amartinezfayo]

I think that in general I prefer to have an err string here as an expected error that can be used to match with the error obtained. Test cases that don't expect errors would have an empty string. Then you can do something like

			if c.err != "" {
				vcs.Require().Equal(err.Error(), c.err)
			} ...

in the assertions to check for the error. I think that allows us to catch some unexpected behavior if the error thrown is different than what we expect.

[hiyosi]

Thanks for review!
Update: 5e0fd1f

[amartinezfayo]

Thank you @hiyosi!
Could you please update the branch so we can merge this?

[hiyosi]

@amartinezfayo Done rebasing the branch with master branch. Thanks!