cherry-pick and merge oauth2 progress from ynqa#20

Merged

clux merged 13 commits intomasterfrom oauth2

Jul 22, 2019

+417-61

Commits on May 24, 2019

Make cluster certificate authority optional

svend
authored and
clux
committed
Add oauth2

ynqa
authored and
clux
committed
Fix signature

ynqa
authored and
clux
committed
Remove unused library
clux
committed
Add credential-plugin authentication support

svend
authored and
clux
committed
Add load_with function to load config with context, cluster, and user

svend
authored and
clux
committed
make it compile
clux
committed

Commits on Jul 18, 2019

Merge branch 'master' into oauth2
clux
authored

Commits on Jul 22, 2019