How do I check to see if my AzureAD version is V1 or V2?

Where would I look to check the AzureAD version? Is there some command line utility that would return the version, or some rest endpoint that gives basic information like that?

Azure AD itself is versionless. What can be v1 or v2 is the endpoint and app registration with which you talk to it.

Check out the docs on the v2 endpoint and a v1 vs v2 comparison

For most URLs (metadata, authorize, token), you can tell based on whether it contains /v2.0/ for example:

https://login.microsoftonline.com/common/oauth2/authorize is v1 whereas https://login.microsoftonline.com/common/oauth2/v2.0/authorize is v2

EDIT - Including extra data points provided by Daniel

The version of your Azure AD application depends on what portal was used to register it,

• If in the Azure Portal, then it's a v1 application.
• If in the App Registration Portal then it's a v2 app.