Hi Olivier,
Due to the privileges which are granted to an external app using the stories and feedback API, management of API keys is restricted to Scrum Masters only.
Regarding being able to look up an API key in general; you will only be able to view an API key on creation; after this it will only be stored in hashed form for security reasons, and you will not be able to view it again. If you no longer know the contents of an API key, you should revoke that key and create a new key instead.
(Note that this is a pretty common security measure, which is used by for example Google as well for granting external applications access to your Google account's information)
Kind regards,
Sjoerd Breur