@Mano K , Yes, you can automate the app creation in Azure AD. The simplest way to deploy apps automatically is to use the AppCreation script that you would be able to find with most of our published sample codes for OAuth and OIDC. Now you can pick that code and modify that according to your requirements.
The main idea that you need to keep in mind is, when you need to register an app, it creates two main objects in AAD, i.e Application Object (Found under App Registration blade) and the registered app's Service Principal Object (can be found under Enterprise Registration Blade). Both the entries would have the same name.
Now using the AppCreation script it uses powershell cmdlets to create these two objects and configure them as needed.
The same concept works for both Applications and Web APIs that you plan to protect or register in AAD.
For SAML apps the steps are little different as for SAML apps you have two available option for configuration:
Now both these options are used mostly to add SAML applications to Azure AD, be it an already hosted app like Salesforce, ServiceNow etc, or a custom SAML app developed in-house.
You can also automate the steps of adding a gallery app but to some extent. You can refer to one of my other posts where the customer had similar requirements for SAML apps automation: https://learn.microsoft.com/en-us/answers/questions/22497/create-saml-application-in-azure-ad-via-powershell.html
Now coming to adding SAML, OAUTH or OIDC apps in ADFS, it totally different from doing it in AAD. Though the concept remains the same, but if you would like to d it with Powershell, cmdlets would change completely.
Hope this helps.
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