Hi Josue,
You have to whitelist the WebIDE as well as all the HTML5 Applications you have in the SuccessFactors IdP.
Point is that when configuring your HCP trial account to trust to SuccessFactors IdP you practically have made each app from your account to be authenticated to SuccessFactors IdP and not to SAP ID Service.
Here is how you can whitelist the WebIDE and the HTML5 Apps:
Procedure
In SuccessFactors Business Execution Suite Provisioning<company_name>Service Provider Settings, choose Authorized SP Assertion Consumer Service Settings.
Choose Add another Service Provider ACS.
In Assertion Consumer Service input field, enter the login URL of your application.
In the Logout URL input field, enter the logout URL of your application. To get the logout URL copy the value of the Location attribute of the SingleLogoutService element of the XML file containing the SAML 2.0 metadata describing SAP HANA Cloud Platform as a service provider. You have downloaded this metadata file when configuring the local service provider settings in the SAP HANA Cloud Platform cockpit.
In the Audience Url input field, enter the name of the local IdP provider (as specified in the local service provider configuration of SAP HANA Cloud Platform).
In the SP Mapping Key input field, enter a unique key name which will be used for integrating the extension application in and registering its site in SuccessFactors EC.
Hope that helps.
Stanimir