Jira Cloud provides apps experience for its users. The apps are not a native, Jira Software apps, build up with Java (and much more) stack as Jira and deployed within Atlassian infrastructure, but they are hosted by apps vendors and whole communication with Jira is done by using iFrames and REST Api provided by Jira Cloud.
Below diagram, shows simplified architecture of how getint.io is cooperates with Jira Cloud.
Getint.io Jira App - its a one of our apps available on Atlassian Marketplace. When its clicked from Apps menu, Jira Cloud will try to load up (Request 1) an iframe with a source from the getint.io platform
Request 1 - it's a request sent by Jira Cloud to getint.io servers in order to load up content within an iframe. That iframe will contain an administration panel of the app where all integrations can be managed as well as whole reporting and other system informations can be accessed. When request is successfully authenticated, UI is loaded up
All the configurations and reporting data, as in every other Jira Cloud app, is hold on getint.io infrastructure servers
Request 2 - getint.io platform to perform data integration is using standard Jira Cloud REST Api. Because all of the requests to Jira Cloud REST Api must be authenticated, during integration setup user is asked to provide user credentials (email and auth token)