Integrating third party platform

[PippaClarkGDS]

Why

Need documentation for users integrating using third-party platforms.

What

New documentation gives guidance on third-party platforms and client_secret_post token authentication method.

Technical writer support

This has been through tech writer review.

How to review

• check out the integrating-third-party-platform branch
• build the content using the new ./build-with-docker.sh script and ensure that the html-proofer step at the end of the build runs cleanly and does not generate any errors that halt the build
• preview the content using ./preview-with-docker.sh to ensure that the new content works in the context of the overall site

Changelog

Changelog has been updated.

Confirm

• [y] I have checked if any docs change here also requires updates to other repositories (ADRs / RFCs, README.md, Team Manual, elsewhere in these docs)
• [y] Where there is any overlap I have updated or opened a PR for corresponding changes

[pauldougan]

@PippaClarkGDS and @sabrinaharris I have maDe two commits to help resolve our pipeline problem as follows:

• added the two urls that were causing issues with html-proofer to the list of exceptions in config.rb so that they don't cause the pipeline to break if the proofer complains, I will raise a jira ticket to capture more investigation into this
• a new convenience script build-with-docker.sh modelled after preview-with-docker.sh to run the middleman build and html-proofer from a Docker container to assist with diagnostics, it will also be a useful script when checking prs local ahead of the final merge

In my view it is better to retain the proofer in the build stage with two exceptions, than to entirely remove the proofer or to prevent it finding legitimate problems that will halt the pipeline.

[pauldougan]

I have raised a Jira story AP-294 to investigate a more comprehensive fix for the pipeline issues