According to my test, we can call Azure DevOps rest API with Azure Ad access token. For more details, please refer to the following steps
Register an Azure AD application
Configure applications
a. Create client secret
b. Configure permissions
Get token
get code
https://login.microsoftonline.com/common/oauth2/v2.0/authorize?
client_id=<app client id>
&response_type=code
&redirect_uri=https://localhost:8000/
&response_mode=query
&scope=499b84ac-1321-427f-aa17-267ca6975798/.default
&state=12345
Get token
Post https://login.microsoftonline.com/common/oauth2/v2.0/token
Content-Type: application/x-www-form-urlencoded
grant_type=authorization_code
&client_id=<>
&code=<>
&redirect_uri=https://localhost:8000/
&scope=499b84ac-1321-427f-aa17-267ca6975798/.default
&client_secret=<>
- Call Rest API
a. list repositories
GET https://dev.azure.com/{organization}/_apis/git/repositories?api-version=6.1-preview.1
Authorization: Bearer <token>
b. List users
GET https://vssps.dev.azure.com/{organization}/_apis/graph/users?api-version=6.1-preview.1
Authorization: Bearer <token>
For further details about Azure DevOps REST Api, please refer to the official document.