Thank you for posting your query on Microsoft Q&A. From above description I could understand that you are looking for way to retrieve Azure AD registered application client secret via Graph API.
Please do correct me if this is not the case by responding in the comments section:
If yes then we have the following answer:
It is not possible to retrieve the client secret via the Microsoft Graph API. The client secret is a confidential value that is generated when you register your application in Azure AD. It is used to authenticate your application with Azure AD and should be kept secret.
Thanks,
Akshay Kaushik
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