Rework onboarding code and add REST controller for integration with the OBW

[jorgeatorres]

Issue: woocommerce/woocommerce-admin#5788

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Description

This PR refactors some of the code in the on-boarding module in order to expose certain internal details that are needed by WooCommerce's onboarding wizard. Also, in order to workaround several limitations in PayPal's partner.js (such as the inability to trigger the popup for dynamically loaded buttons, certain issues with Firefox, etc.), onboarding.js was heavily modified too.

To permit integration with WooCommerce's onboarding wizard, a REST controller was also added. In particular, this controller exposes the following routes:

• /wc-paypal/v1/onboarding/get-params [POST]
  Returns information useful for presenting the user with a sign-up link/button.

  • Parameters (JSON):
    • environment: either 'sandbox' or 'production'. Optional. Defaults to 'sandbox'.
  • Response (JSON):
    • environment: Environment for which the parameters apply.
    • scriptURL: URL to the onboarding.js script.
    • scriptData: Data required by the onboarding.js script. Should be added to the PayPalCommerceGatewayOnboarding variable in the global context.
    • onboardCompleteCallback: Value to be used for the data-paypal-onboard-complete attribute in the sign-up link or button.
    • signupLink: Generated sign-up link. Final redirect URL defaults to the settings page.

• /wc-paypal/v1/onboarding/get-status [GET]
  Returns information about the current onboarding status.

  • Parameters (JSON): N/A.
  • Response (JSON):
    • environment: Current environment.
    • onboarded: true if onboarded was completed for the current environment.
    • state: Textual representation of the current onboarding status ("start", "progressive", "onboarded").
    • sandbox.onboarded: Same as onboarded but for the "sandbox" environment in particular.
    • sandbox.state: Same as state but for the "sandbox" environment in particular.
    • production.onboarded: Same as onboarded but for the "production" environment in particular.
    • production.state: Same as state but for the "production" environment in particular.

• /wc-paypal/v1/onboarding/set-credentials [POST]
  Allows setting credentials for a given environment and also enables the gateway.

  • Parameters (JSON):
    • environment: Environment the credentials apply to. Required.
    • merchant_id: Merchant ID. Required.
    • merchant_email: Merchant e-mail. Required.
    • client_id: API Client ID. Required.
    • client_secret: API Client Secret. Required.
  • Response (JSON): Empty or error in case of error (missing fields etc.).

Steps to test:

Make sure the usual onboarding flow works correctly

1. Go to WC > Settings > Payments > PayPal.
2. Disconnect (if connected).
3. Click "Connect to PayPal" or "Connect to PayPal Sandbox" (depending on whether you have sandbox enabled or not).
4. A popup should appear and you should be able to complete the onboarding flow.
5. After clicking to return to the site at the final step of the process, you should be back at the settings screen, with all credential fields correctly filled out.
6. Perform a test purchase from the frontend to confirm.
7. (Optional) Repeat the above but for the other mode (sandbox/production).

Test the REST endpoints

1. Go to WC > Settings > Advanced > REST API and create an API key for testing. It should be for a user with sufficient access (i.e. "install_plugins" capability).

2. Keep key and secret handy.

3. Make sure the endpoints work correctly. Test with different inputs. Some example requests:

   cURL command	Expected output
   curl -X GET https://SITE/wp-json/wc-paypal/v1/onboarding/get-status -u API_KEY:API_SECRET	Onboarding status as described above
   curl -X POST https://SITE/wp-json/wc-paypal/v1/onboarding/get-params -u API_KEY:API_SECRET	Onboarding parameters (signup link, environment, etc.) as describe above
   curl -X POST https://SITE/wp-json/wc-paypal/v1/onboarding/set-credentials -u API_KEY:API_SECRET -H 'content-type: application/json' -d '{"environment":"whatever"}'	Error due to invalid environment.
   curl -X POST https://SITE/wp-json/wc-paypal/v1/onboarding/set-credentials -u API_KEY:API_SECRET -H 'content-type: application/json' -d '{"environment":"sandbox","merchant_id":"MERCHANTID","client_id":"CLIENTID"}'	Error due to missing fields "merchant_email" and "client_secret".
   curl -X POST https://SITE/wp-json/wc-paypal/v1/onboarding/set-credentials -u API_KEY:API_SECRET -H 'content-type: application/json' -d '{"environment":"sandbox","merchant_id":"MERCHANTID","merchant_email":"MERCHANTEMAIL","client_id":"CLIENTID","client_secret":"CLIENTSECRET"}'	No error. Confirm credentials were set on the settings screen.

[chickenn00dle]

Nice work @jorgeatorres!

I tested the onboarding flow for sandbox and production and there were no issues. I also tested each endpoint individually and everything checks out.

Since @mattallan mentioned he'd also review this, I won't merge so he can also have a look.

[mattallan]

Nice one @jorgeatorres! I've tested all those API endpoints as well as the normal onboarding flow and it's all working perfectly from my end.

This is good to merge ! 💯

[strangerkir]

Looks good to me.

[strangerkir]

Probably, it makes sense to use esc_html__ instead of just __.

[jorgeatorres]

Thank you all for the reviews! Merging now.