Enables optional handling of PKCE

[edgar89]

Some OAuth provider do not have support for PKCE. This PR uses a feature flag to use/not use PKCE-specific fields during OAuth process.

Default is the current behaviour where PKCE is enabled

[CLAassistant]

All committers have signed the CLA.

[lmangani]

Thanks for the contribution @edgar89 we appreciate it!
Please sign the CLA so we can review and merge the change 👍

[edgar89]

Thanks for the contribution @edgar89 we appreciate it! Please sign the CLA so we can review and merge the change 👍

Hello @lmangani I think I did that, I don't know why it is still reported as unsigned

[lmangani]

Hello @lmangani I think I did that, I don't know why it is still reported as unsigned

Thanks @edgar89 are you sure its the same email used for the commits was used to sign the CLA?

[skyreginag]

Hello @lmangani I think I did that, I don't know why it is still reported as unsigned

Thanks @edgar89 are you sure its the same email used for the commits was used to sign the CLA?

Yeah, sorry about that - I commited using company account and opened the PR using my personal account. Now it should be all ok

[lmangani]

Thank you Giuseppe @edgar89
@adubovikov please review and merge 👍

[adubovikov]

Thank you!