I am trying to implement Azure API Management APIs using Microsoft.Azure.Management.ApiManagement
4.0.4-preview.
No where I see documentation for implementa
copied bear token from https://docs.microsoft.com/en-us/rest/api/apimanagement/user/get by logging proper user name and password
It seems that there is something wrong with the way you generate.
The authorization header should be a JSON Web Token that you obtain from Azure Active Directory, but directly from Azure Portal. For more details, you could refer to this article.
You can refer to this document for how to obtain a JWT from AAD and protect an API by using OAuth 2.0 with Azure Active Directory and API Management.