Register app with Azure AD through developer portal
Given that there are already integrations with Azure AD, it would be developer friendly if you could register and manage your apps with Azure AD through the developer console.
That way you would need just one portal to deal with things like client ids, secrets etc
Bryan Coller commented
I think it makes sense if an API is secured with OAuth2, the developer portal should allow the user to create a "client application" which underneath creates the Azure AD application (along with the client secret). This seems to be the norm in how most API Management vendors (along with companies like Facebook who expose public API's) allow self-servicing the creation of client id/secret parameters.