Clarification on OAuth2 Authentication - grant_type = password

Question

Hi Everyone,

I'm currently working on triggering an API (Fabric Job Scheduler in this case), which, as of now, doesn't support service principal authentication. To work around this, I've been trying to obtain an Access Token for an indivisual user without MFA using the following endpoint:

https://login.microsoftonline.com/<tenant>/oauth2/v2.0/token

Here's the body of the request I'm using:

client_id=<clientid>&username=<username>&password=<password>&scope=https://api.fabric.microsoft.com/Workspace.ReadWrite.All https://api.fabric.microsoft.com/Item.ReadWrite.All https://api.fabric.microsoft.com/DataPipeline.Execute.All&grant_type=password

However, I encountered an issue where it seems that I also need to include the client secret in the request body to successfully retrieve the Access Token.

I've noticed that the requirement for both the client secret and user credentials is mentioned in the Microsoft documentation (referencing the [ OAuth 2.0 Resource Owner Password Credentials grant type ]).

I'm trying to understand the rationale behind requiring both user credentials (username and password) as well as client credentials (Client ID and Client Secret) for authentication in this scenario. What is the purpose of combining these two forms of authentication, and are there specific security or operational reasons for this requirement?

Any insights or explanations would be greatly appreciated.

Thank you!

Answer 1

Hello @Ahwan Mishra,

Thank you for posting your query on Microsoft Q&A.

Based on your description, I understand that you're generating an access token using the ROPC (Resource Owner Password Credentials) grant flow and specifying Fabric APIs as a scope. However, when sending a POST request to obtain a token using the ROPC flow with the client ID, scope, username, and password (with grant_type set to password), you encountered an invalid_client error stating, "AADSTS7000218: The request body must contain the following parameter: 'client_assertion' or 'client_secret'."

When you included the client secret in the POST request, the access token was generated without any errors.

I'm trying to understand the rationale behind requiring both user credentials (username and password) as well as client credentials (Client ID and Client Secret) for authentication in this scenario. What is the purpose of combining these two forms of authentication, and are there specific security or operational reasons for this requirement?

To clarify, the ROPC and Client Credentials flows are not typically combined. When the grant_type is set to password, it should only utilize the ROPC flow, not a combination with the Client Credentials flow.

Regarding the need for a client_secret when sending a POST request to obtain a token: If your app is a public client, the client_secret or client_assertion cannot be included. However, if the app is a confidential client, then including the client_secret is mandatory. This is because Microsoft identity platform and OAuth 2.0 have specific requirements for confidential clients.Microsoft identity platform and OAuth 2.0 Resource Owner Password Credentials

Your application should allow public client flows. If this option is not enabled for your application, and you are using the ROPC flow to obtain a token, then the client_secret parameter is required in the request body.

Please check whether the "Allow public client flows" option is enabled for your application. If it is not enabled, as mentioned above, the client_secret parameter must be included in the request body. I hope this information is helpful. Please feel free to reach out if you have any further questions.

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment". Thanks,

Raja Pothuraju.