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Difference between the "Resource Owner Password Flow" and the "Client Credentials Flow"

The difference between the "Resource Owner Password Flow" and the "Client Credentials Flow" seems unclear to me. The former seems to forward the password credentials to the server for verification, while the latter does authenticate with the server in some way too, but the spec doesn't specify what method is used here. Is this flow designed for cookie sessions? The spec doesn't really provide a clear use case.

From the OAuth 2.0 spec:

 +---------+                                  +---------------+
 |         |                                  |               |
 |         |>--(A)- Client Authentication --->| Authorization |
 | Client  |                                  |     Server    |
 |         |<--(B)---- Access Token ---------<|               |
 |         |                                  |               |
 +---------+                                  +---------------+

                 Figure 6: Client Credentials Flow

and

 +----------+
 | Resource |
 |  Owner   |
 |          |
 +----------+
      v
      |    Resource Owner
     (A) Password Credentials
      |
      v
 +---------+                                  +---------------+
 |         |>--(B)---- Resource Owner ------->|               |
 |         |         Password Credentials     | Authorization |
 | Client  |                                  |     Server    |
 |         |<--(C)---- Access Token ---------<|               |
 |         |    (w/ Optional Refresh Token)   |               |
 +---------+                                  +---------------+

        Figure 5: Resource Owner Password Credentials Flow

r
rcabr

The client credentials flow only requires the client_id and client_secret. The Resource Owner flow requires the user's password.

The client credentials flow allows an application to get a token w/out the context of the user.


But still unclear how to get Authorization (client_id and client_secret)
Please note that RO flow is not recommended anymore scottbrady91.com/OAuth/…
*The Resource Owner flow requires the user's password." - I think it's helpful to clarify this a bit more. The Resource Owner flow requires the user's username, password, and the client's client_id and client_secret.
S
StephenPAdams

A good example of this would be the following:

Suppose you're a statistics company called AllStats that has its own user base where each user has their own username and password. AllStats has its own existing website which dogfoods its own API. However, AllStats now wants to release a mobile app.

Since the mobile app will be a 1st party application (see: developed by AllStats), the Resource Owner Password Flow makes a lot of sense. You'll want the user to get a screen (username, password) that flows with the app instead of kicking them over to an auth server (and then back into the app). Users will trust the application when they enter their username/password because it's a 1st party app.

I like to look at the Resource Owner Password Flow as a flow that 1st party app developers would use, whereas the Client Credentials Flow a flow that 3rd party app developers would use.

Imagine if the Facebook app required you to use the Client Credentials Flow instead of just presenting you with a username/password form. Would seem a little odd, yeah?

Now, if imagine you download a 3rd party app that had Facebook integration. I'd imagine you (and most people) would be very leery if the app was prompting you for a username/password instead of using the Client Credential Flow UI.

FWIW, this isn't to say that 1st party apps don't use the Client Credential Flow. But rather to try and paint a real world scenario (and overall generalization) of when Resource Owner Password Flow would be used.


I think you're confusing the "Client credentials" flow with the "Authorization code" grant. In fact, the "Client credentials" grant doesn't even ask for username/password and has no "client credential UI" as you mentioned, because it's used for machine-to-machine authentication.
the part about 1st party apps and Resource Owner Password Flow is clear and correct, but maybe you have mistaken Client Credential Flow with the Implicit Flow ?
I don't prefer to use Resource Owner Password for Mobile application because It's a public Client (your client secret could be revealed at resource-owner site). So that bad-guy, can use this Resource Owner Password flow to do a brute force password attack. I think Owner Password Flow should be used in 1st app as a private client only.
Ok, so I am implementing 1st party mobile application for my business needs. Mobile application is a kind of private - it is developed within my business. I also got web application with same characteristics. I need API for next level of layered system - can I use resource owner password flow for authentication ? I know OAuth defines authorization, not authentication, but what is wrong with this solution ? Thanks
There is no Client Credential Flow UI
C
Community

Besides user3287829's answer. I want to add the following.

As the RFC said about Client Credential grant.

The client makes a request to the token endpoint by adding the following parameters using the "application/x-www-form-urlencoded" format per Appendix B with a character encoding of UTF-8 in the HTTP request entity-body: grant_type REQUIRED. Value MUST be set to "client_credentials". scope OPTIONAL. The scope of the access request as described by Section 3.3. The client MUST authenticate with the authorization server as described in Section 3.2.1. For example, the client makes the following HTTP request using transport-layer security (with extra line breaks for display purposes only): POST /token HTTP/1.1 Host: server.example.com Authorization: Basic czZCaGRSa3F0MzpnWDFmQmF0M2JW Content-Type: application/x-www-form-urlencoded grant_type=client_credentials The authorization server MUST authenticate the client.

The client must be registered in the authorization server in advance. and Authorization includes the client credential which will be authenticated by the server.


f
fallincode

This is the closest answer to the question. However, none of the answers provide a clearer example:

You must use the Client Credentials Grant when a machine needs access to resources it owns on another machine. It is necessary to use the Resource Owner Password Credentials Grant (actually not, it is better to use the Authorization Code Grant) when the machine needs to access resources that belong to the end user (not the machine) on behalf of that user.

The key question you should ask yourself when choosing between these two flows is who owns the resource to be accessed. If it belongs to the machine (client), then you need the first option, if it does not belong to the machine, but belongs to the user on whose behalf the machine will execute requests, then you need the second option.


T
Tharsanan

Other answers explain well about the "Resource Owner Password Flow". So I will explain the "Client_credentials" grant type flow. In the "Client_credentials" flow client_id and client_secret are used to authenticate the Client not the Resource owner. So you can ask without the Resource owner authentication how a client (Most of the time a application) will obtain access to the resources. That's a good question. The answer is, here Client will get access_token for it's own resources or access to an user-resource which is already given under this client_id. client_secret and client_id generation is a most of the time a manual process. For example look at this -> Create a client ID and client secret for google APIs. In the Client secret creation step you are creating authentication credential for your application.


E
Eduardo Fabricio

additionally, in terms of auditing, resource owner is better way, because you can identify by access_token which specific user is calling your api through the client application, while client_credential identifies only the application client


Isn't identifying(/authenticating) the user completely out of scope of OAuth2? "OAuth 2.0 is not an authentication protocol". I suppose OpenID Connect is the best match for authentication on top of OAuth 2.
You shouldn't be using ROPC in most cases scottbrady91.com/OAuth/…
the whole point of client credentials is that there is no concept of the user, so not sure where you are going with this
In fact, there are some use cases that doesnt have a user participation and interacting with the system, however i have been seen a lot of examples that there is a Specific User interacting into System "A" and the System "A" calls the System "B" in this case, i prefer to try indetify the specific user if it is possible of course. So, i'm no critisizing the OAuth 2 client-credential protocol, i'm only explaning that the lazy way is client credentials in some cases that is possible to consider authenticate the specific user bwteen 2 systems.. do you got it ? it is my viewpoint.
however it is a very old post ! lol, and nowadays there are some articles about a lot of questions with oauth2 use, and security problems.