OpenText server - how to handle Azure authentication with API REST?

Question

We used to connect to OpenText server through the REST API. It worked well as long as we used Active Directory authentication. However, after migrating to Azure AD, the following .Net code (that used to work) returns an “Invalid user/password” error:

Using our new Azure “username” and “password” in the code below:

 Dim reader As StreamReader = Nothing
 Dim oRequest As HttpRequestMessage = Nothing
 Dim oHTTPClient As HttpClient = Nothing
 Dim oResponse As HttpResponseMessage = Nothing

 oRequest = New HttpRequestMessage(HttpMethod.Post, "HTTPS://****/api/v1/auth")
 postData = "username=" & username & "&password=" & password
 oRequest.Content = New StringContent(postData, Text.Encoding.UTF8, "application/x-www-form-urlencoded")

 oHTTPClient = New HttpClient
 oResponse = oHTTPClient.Send(oRequest)
 reader = New StreamReader(oResponse.Content.ReadAsStream())
 responseFromServer = reader.ReadToEnd()

At this point, “responseFromServer” is {""error"":""Invalid username/password specified.""}