feat: document LINE social sign-in provider

[David-Wobrock]

Document how to set up a LINE social sign-in.

Related Issue or Design Document

Relates to ory/kratos#4240

Checklist

• I have read the contributing guidelines and signed the CLA.
• I have referenced an issue containing the design document if my change introduces a new feature.
• I have read the security policy.
• I confirm that this pull request does not address a security vulnerability.
  If this pull request addresses a security vulnerability,
  I confirm that I got approval (please contact security@ory.sh) from the maintainers to push the changes.
• I have added tests that prove my fix is effective or that my feature works.
• I have added the necessary documentation within the code base (if appropriate).

Further comments

[David-Wobrock]

Thanks @vinckr for the patch 🙏

[vinckr]

lgtm :)

[alnr]

Hey @David-Wobrock !
ory/kratos#4240 was just merged to master. Would you mind rebasing this PR? We've done some restructuring to the docs in the meantime. Thank you!

[David-Wobrock]

Hey @David-Wobrock ! ory/kratos#4240 was just merged to master. Would you mind rebasing this PR? We've done some restructuring to the docs in the meantime. Thank you!

Sure! Conflicts are fixed ✔️ I pushed the changes :)

[vinckr]

lgtm
didnt test the provider

[David-Wobrock]

didnt test the provider

We have been running a fork of Kratos in production with ory/kratos#4240 for a while now.
I can confirm it works 😁

With a configuration like:

                - id: line
                  provider: line
                  auth_url: https://access.line.me/oauth2/v2.1/authorize
                  issuer_url: https://access.line.me
                  mapper_url: file:///etc/config/line_mapping.jsonnet
                  token_url: https://api.line.me/oauth2/v2.1/token
                  client_id: placeholder-filled-by-env-config
                  client_secret: placeholder-filled-by-env-config
                  scope:
                    - email
                    - openid
                    - profile

[vinckr]

playwright tests are failing it seems because we are coming from an repo outside of ory org.
but i think its fine, once the upstream is released we can merge even though they fail, this doesn't touch the code examples.