Remove dependency on "golang.org/x/oauth2"

[WillAbides]

Resolves#2893

This removes the primary module's dependency on "golang.org/x/oauth2" and replaces it with a RoundTripper that adds an "Authorization" header with the value "Bearer ".

TestNewTokenClient now does an http request and checks for the "Authorization" header.

I moved roundTripperFunc from test code to prod because it was useful for creating the RoundTripper.

[codecov]

Codecov Report

Merging #2895 (9454fd3) into master (38ca69f) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@ Coverage Diff @@## master #2895 +/- ##
=======================================
Coverage 98.10% 98.10% =======================================
Files 142 142 Lines 12340 12347 +7 =======================================
+ Hits 12106 12113 +7 
Misses 159 159 Partials 75 75 

Files Changed	Coverage Δ
github/github.go	98.00% <100.00%> (+0.02%)	⬆️

[gmlewis]

Do you want to update all the files that mention oauth2, including documentation, while you're here?

$ rg -l oauth2
README.md
go.sum
scrape/go.sum
example/newreposecretwithlibsodium/go.sum
example/newreposecretwithlibsodium/go.mod
go.mod
github/github.go
github/doc.go
example/go.sum
example/go.mod
example/tokenauth/main.go
example/newfilewithappauth/main.go
github/github_test.go

[WillAbides]

These are the remaining oauth2 mentions:

$ rg -l oauth2
README.md
github/github.go
github/doc.go
example/go.sum
example/go.mod
example/newfilewithappauth/main.go
scrape/go.sum

The first three are docs and code comments about how to authenticate. I think it's appropriate to keep oauth2 there because go-github doesn't offer an Enterprise equivalent of NewTokenClient.

example/* is similar to the doc issue except this time it's actually using oauth2 as an example. Fortunately example is its own module so we don't need to worry about extra imports from there.

scrape/go.sum has an oauth2 line because scrape/go.mod requires "github.com/google/go-github/v54 v54.0.0" which still requires oauth2. That should go away the first time go mod tidy is run in scrape/ after this change is released.

[gmlewis]

Normally the maintainers perform the "go mod tidy", and we have been using "go mod tidy -compat=1.17" for a long while now.

But all the tests seem to be passing, so maybe we are still fine. This will be an experiment. 😄

Thank you, @WillAbides !
LGTM.

Awaiting second LGTM+Approval from any other contributor to this repo before merging.

[gmlewis]

scrape/go.sum has an oauth2 line because scrape/go.mod requires "github.com/google/go-github/v54 v54.0.0" which still requires oauth2. That should go away the first time go mod tidy is run in scrape/ after this change is released.

Thanks for the reminder! I should do that anyway.

Doh, I gotcha. I misread that before, but now I understand. Thanks.

[gmlewis]

Thank you, @gabriel-samfira !
Merging.