I am self answering this to make life easier and more joyful for us developers to find this information, as I personally found that there was lots of info to go through.
How to login with username/password (end-user credentials) using OAuth2 and Microsoft login https://login.microsoftonline.com/{app-id}/oauth2/token
Microsoft does not recommend passing username/password information for endusers. That is why they dont post guides for this. For security reason they want you to use the redirection to their login page. Use https://login.microsoftonline.com/{tenant-id}/oauth2/authorize to get there.
However it is possible and very easy to do this using their oauth2 rest api.
Create an http request to
base url: https://login.microsoftonline.com/{tenant-id}/oauth2/token
{tenant-id} //obtained from AzureAD config section
Use the following request parameters in the body section
grant_type = password //read up on the other grant types, they are all useful, client_credentials and authorization_code
client_id = {client-id}//obtained from the application section in AzureAD
client_secret = {client-secret}//obtained from the application section in AzureAD
resource = https://graph.microsoft.com //there is also the api https://graph.windows.net, use the latest and best one
username = {enduser-username} //example rofler@domain.onmicrosoft.com
password = {enduser-password} //example Hs782f8a
A successful response should include the access_token and refresh_token
Tested in year 2016
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