Modify module path to github.com/go-oauth2/oauth2/v4

Upgrade to oauth2.v4

Remove naked returns

Merge conflict

Merge pull request go-oauth2#125 from dmcinnes/support-refresh-tokens…

…-that-do-not-expire

Support access and refresh tokens that do not expire

Fixed jwt test

Merge pull request go-oauth2#102 from jakubknejzlik/patch-1

User JWT standard claims

Fixed optional for redirect_uri under code authorization

Add refresh token example

Add go mod