Integrate custom web page (form) to Dynamics CRM Online Portal

Hello,

is it possible to develop custom web page and integrate it to portal? 

For example:

We would like to develop web page with form for inserting some registration data. After data are inserted, user has to click submit button to execute business logic. At first validation process is executed (checking some CRM data) and if everything is OK new record is created. If validation was not successful, error message should be shown to user.

This custom page could be hosted on our server or in Azure if it is required by Portal.

Thank you for your help,

Matej