Add support for allowed_idps feature on Cloudflare Access

[xens]

Goal of this issue is to track the implementation of this missing feature allowed_idps inside the Cloudflare Terraform provider - Access Application resource.

For now this feature is not yet supported inside the cloudflare-go library (WIP -> cloudflare/cloudflare-go#483). When it'll be done we'll be able to work on the Cloudflare Terraform provider implementation.

Ref:

• https://api.cloudflare.com/#access-applications-properties

[xens]

@jacobbednarz I'm not 100% sure how to handle the acceptance tests, ideally I'd create an Access application and specify the IdP UUID into it and then verify that the correct UUID has been set but I don't know if we already have a fake IdP that is defined on our test account that I can reuse ?

[jacobbednarz]

You can create a dependant resource in your test and reference that. Providing the test exits cleanly, you'll also clean up those resources.

[jacobbednarz]

Here is a good example

https://github.com/terraform-providers/terraform-provider-cloudflare/blob/acf56bcf46cc5cde9a94d3fc696c88162297718c/cloudflare/resource_cloudflare_firewall_rule_test.go#L69

[xens]

Linked to PR #734

[jacobbednarz]

Closed in #734