Re: [OAUTH-WG] OAuth 2.1: dropping password grant

[Neil Madden <[e-mail]>]

But again, I’m talking about existing deployments. If you have an existing deployment using ROPC with service accounts and you have tens or hundreds of thousands of such accounts, this really sounds like a lot of work to change over. 

I forgot one of the other reasons for preferring a service account over an OAuth 2 client - some features of OAuth/OIDC require client secrets to be recoverable on the AS. For example, if you request an ID token signed with HMAC in an implicit/hybrid OIDC flow then this is signed using the client secret as the HMAC key. This prevents the AS from hashing the client secret, so client_credentials grant introduces security weaknesses compared to an ROPC service account flow. So you’d really want to move both to client_credentials flow and a more secure authentication mechanism - e.g. mTLS, and public key signed/encrypted ID tokens.

(NB: this is not just due to the implicit grant - e.g., CIBA backchannel auth in push mode has the same issue if you use HMAC-signed ID tokens).

— Neil


> On 22 Feb 2020, at 01:05, Richard Backman, Annabelle <[e-mail]> wrote:
> 
> ROPC without a client ID or authentication is functionally equivalent to Client Credentials grant with client secret authentication in the request body. You've just renamed "client_id" to "username" and "client_secret" to "password".
> 
> The AS simply needs to be able to resolve the client ID to the service account. You could use any of the following strategies, depending on the environment:
> * Use service account identifiers as client IDs
> * Use encrypted blobs containing service account identifiers as client IDs, so someone can't choose a client ID by creating a service account with a specific identifier
> * Use opaque values that the AS can resolve to service account identifiers, e.g., via a database lookup
> 
> If the AS needs the service account's password because it's authenticating against a legacy system, then use the service account password as the client secret. Stack mTLS on top, if you want. If the AS just needs to resolve the account so it can put it in tokens that RSes will look at, then you can use whatever client authentication mechanism you want.
> 
> Is there a scenario I'm missing here?
> 
> –
> Annabelle Backman (she/her)
> AWS Identity
> https://aws.amazon.com/identity/
> 
> 
> On 2/21/20, 1:53 PM, "Neil Madden" <[e-mail]> wrote:
> 
>    The AS doesn’t issue the service account IDs, that’s the whole point - integration with existing systems. Lot’s of people don’t have the luxury of rebuilding systems from scratch to fit in with the preferences of the OAuth WG.
> 
>    ROPC doesn’t require client authentication, or even a client identifier. If you’re using a service account you indeed don’t need to bother issuing client credentials. The same is true when using the JWT bearer grant. If you want to increase security you can use cert-bound access tokens.
> 
>> On 21 Feb 2020, at 20:28, Richard Backman, Annabelle <[e-mail]> wrote:
>> 
>> The client IDs can still be opaque identifiers provided by the AS, they just happen to be associated with specific service accounts. Or they could be the opaque IDs that the AS already issued for the service account. Either way, the AS could issue a token with the appropriate subject and other claims for the service account.
>> 
>> If your client identity is bound to a specific service account identity (i.e., the resource owner), then ROPC reduces down to Client Credentials. What's the point in passing two identifiers and two credentials for the same identity?
>> 
>> –
>> Annabelle Backman (she/her)
>> AWS Identity
>> https://aws.amazon.com/identity/
>> 
>> 
>> On 2/21/20, 6:48 AM, "OAuth on behalf of Neil Madden" <[e-mail] on behalf of [e-mail]> wrote:
>> 
>>   Sorry, I missed that message. 
>> 
>>   While this may be a solution in specific circumstances, I don’t think it’s a general solution. e.g. an AS may not allow manually choosing the client_id to avoid things like https://tools.ietf.org/html/draft-ietf-oauth-security-topics-14#section-4.13 or may return different introspection results for client credentials tokens (e.g. with no “sub”) and so on. In practice, this adds even more steps for somebody to migrate from existing ROPC usage.
>> 
>>   This is asking people to make fundamental changes to their identity architecture rather than simply switching to a new grant type.
>> 
>>   — Neil
>> 
>>> On 21 Feb 2020, at 14:34, Torsten Lodderstedt <[e-mail]> wrote:
>>> 
>>> I see - we have gone full cycle :-) 
>>> 
>>> Annabelle’s proposal would solve that. Relate a client id to a service account and obtain the token data from there. 
>>> 
>>>> On 21. Feb 2020, at 15:31, Neil Madden <[e-mail]> wrote:
>>>> 
>>>> Yes, that is great. But mTLS doesn’t support service accounts (!= clients). Maybe it should? Should there be a mTLS *grant type*?
>>>> 
>>>> — Neil
>>>> 
>>>>> On 21 Feb 2020, at 14:20, Torsten Lodderstedt <[e-mail]> wrote:
>>>>> 
>>>>> Have you ever tried the client credentials grant with mTLS? After reading your description it seems to be simpler than JWT Bearer.
>>>>> 
>>>>> * work out if the AS even supports mTLS
>>>>> * work out how to configure the AS to trust my cert(s)
>>>>> * Create key pair and cert using openssl
>>>>> * Register your (self-signed) cert along with your client_id
>>>>> * Configure the HTTP client to use your key pair for TLS Client Authentication
>>>>> 
>>>>> Works very well for us. 
>>>>> 
>>>>>> On 21. Feb 2020, at 15:12, Neil Madden <[e-mail]> wrote:
>>>>>> 
>>>>>> No failures, but it is a much more complex grant type to set up, when you consider everything you have to do:
>>>>>> 
>>>>>> * work out if the AS even supports JWT bearer and how to turn it on
>>>>>> * work out how to configure the AS to trust my public key(s)
>>>>>> - do I have to create a new HTTPS endpoint to publish a JWK Set?
>>>>>> * determine the correct settings for issuer, audience, subject, etc. Does the AS impose non-standard requirements? e.g. RFC 7523 says that the JWT MUST contain a “sub” claim, but Google only allows this to be present if your client is doing impersonation of an end-user (which requires additional permissions).
>>>>>> * do I need a unique “jti” claim? (OIDC servers do, plain OAuth ones might not) If I do, can I reuse the JWT or must it be freshly signed for every call?
>>>>>> * locate and evaluate a JWT library for my language of choice. Monitor that new dependency for security advisories.
>>>>>> * choose a suitable signature algorithm (‘ere be dragons)
>>>>>> * figure out how to distribute the private key to my service
>>>>>> 
>>>>>> Compared to “create a service account and POST the username and password to the token endpoint” it adds a little friction. (It also adds a lot of advantages, but it is undeniably more complex).
>>>>>> 
>>>>>> — Neil
>>>>>> 
>>>>>> 
>>>>>>> On 21 Feb 2020, at 13:41, Matthew De Haast <matt=[e-mail]> wrote:
>>>>>>> 
>>>>>>> I have a feeling that if we had more concise JWT libraries and command line tools, where using the JWT Bearer grant became a one-liner again then we wouldn’t be having this conversation. So perhaps removing it is an incentive to make that happen.
>>>>>>> 
>>>>>>> Neil could you elaborate more on this please. What failures are you currently experiencing/seeing with the JWT Bearer grant? 
>>>>>>> 
>>>>>>> Matt
>>>>>>> 
>>>>>>> On Thu, Feb 20, 2020 at 12:42 AM Neil Madden <[e-mail]> wrote:
>>>>>>> I have a feeling that if we had more concise JWT libraries and command line tools, where using the JWT Bearer grant became a one-liner again then we wouldn’t be having this conversation. So perhaps removing it is an incentive to make that happen.
>>>>>>> 
>>>>>>> 
>>>>>>>> On 19 Feb 2020, at 22:01, Dick Hardt <[e-mail]> wrote:
>>>>>>>> 
>>>>>>>> Neil: are you advocating that password grant be preserved in 2.1? Or do you think that service account developers know enough about what they are doing to follow what is in 6749?
>>>>>>>> ᐧ
>>>>>>>> 
>>>>>>>> On Wed, Feb 19, 2020 at 1:52 PM Neil Madden <[e-mail]> wrote:
>>>>>>>> OAuth2 clients are often private to the AS - they live in a database that only the AS can access, have attributes specific to their use in OAuth2, and so on. Many existing systems have access controls based on users, roles, permissions and so on and expect all users accessing the system to exist in some user repository, e.g. LDAP, where they can be looked up and appropriate permissions determined. A service account can be created inside such a system as if it was a regular user, managed through the normal account provisioning tools, assigned permissions, roles, etc.
>>>>>>>> 
>>>>>>>> Another reason is that sometimes OAuth is just one authentication option out of many, and so permissions assigned to service accounts are preferred over scopes because they are consistently applied no matter how a request is authenticated. This is often the case when OAuth has been retrofitted to an existing system and they need to preserve compatibility with already deployed clients.
>>>>>>>> 
>>>>>>>> See e.g. Google cloud platform (GCP): https://developers.google.com/identity/protocols/OAuth2ServiceAccount
>>>>>>>> They use the JWT bearer grant type for service account authentication and assign permissions to those service accounts and typically have very broad scopes. For service-to-service API calls you typically get an access token with a single scope that is effectively “all of GCP” and everything is managed at the level of permissions on the RO service account itself. They only break down fine-grained scopes when you are dealing with user data and will be getting an access token approved by a real user (through a normal auth code flow).
>>>>>>>> 
>>>>>>>> — Neil
>>>>>>>> 
>>>>>>>>> On 19 Feb 2020, at 21:35, Torsten Lodderstedt <[e-mail]> wrote:
>>>>>>>>> 
>>>>>>>>> Can you explain more in detail why the client credentials grant type isn’t applicable for the kind of use cases you mentioned?
>>>>>>>>> 
>>>>>>>>>> Am 19.02.2020 um 22:03 schrieb Neil Madden <[e-mail]>:
>>>>>>>>>> 
>>>>>>>>>> I very much agree with this with regards to real users. 
>>>>>>>>>> 
>>>>>>>>>> The one legitimate use-case for ROPC I’ve seen is for service accounts - where you essentially want something like client_credentials but for whatever reason you need the RO to be a service user rather than an OAuth2 client (typically so that some lower layer of the system can still perform its required permission checks).
>>>>>>>>>> 
>>>>>>>>>> There are better grant types for this - e.g. JWT bearer - but they are a bit harder to implement. Having recently converted some code from ROPC to JWT bearer for exactly this use-case, it went from a couple of lines of code to two screens of code. For service to service API calls within a datacenter I’m not convinced this resulted in a material increase in security for the added complexity.
>>>>>>>>>> 
>>>>>>>>>> — Neil
>>>>>>>>>> 
>>>>>>>>>>> On 18 Feb 2020, at 21:57, Hans Zandbelt <[e-mail]> wrote:
>>>>>>>>>>> 
>>>>>>>>>>> I would also seriously look at the original motivation behind ROPC: I know it has been deployed and is used in quite a lot of places but I have never actually come across a use case where it is used for migration purposes and the migration is actually executed (I know that is statistically not a very strong argument but I challenge others to come up with one...)
>>>>>>>>>>> In reality it turned out just to be a one off that people used as an easy way out to stick to an anti-pattern and still claim to do OAuth 2.0. It is plain wrong, it is not OAuth and we need to get rid of it.
>>>>>>>>>>> 
>>>>>>>>>>> Hans.
>>>>>>>>>>> 
>>>>>>>>>>> On Tue, Feb 18, 2020 at 10:44 PM Aaron Parecki <[e-mail]> wrote:
>>>>>>>>>>> Agreed. Plus, the Security BCP is already effectively acting as a grace period since it currently says the password grant MUST NOT be used, so in the OAuth 2.0 world that's already a pretty strong signal..
>>>>>>>>>>> 
>>>>>>>>>>> Aaron
>>>>>>>>>>> 
>>>>>>>>>>> 
>>>>>>>>>>> 
>>>>>>>>>>> On Tue, Feb 18, 2020 at 4:16 PM Justin Richer <[e-mail]> wrote:
>>>>>>>>>>> There is no need for a grace period. People using OAuth 2..0 can still do OAuth 2.0. People using OAuth 2.1 will do OAuth 2.1. 
>>>>>>>>>>> 
>>>>>>>>>>> — Justin
>>>>>>>>>>> 
>>>>>>>>>>>>> On Feb 18, 2020, at 3:54 PM, Anthony Nadalin <tonynad=[e-mail]> wrote:
>>>>>>>>>>>> 
>>>>>>>>>>>> I would suggest a SHOULD NOT instead of MUST, there are still sites using this and a grace period should be provided before a MUST is pushed out as there are valid use cases out there still.
>>>>>>>>>>>> 
>>>>>>>>>>>> From: OAuth <[e-mail]> On Behalf Of Dick Hardt
>>>>>>>>>>>> Sent: Tuesday, February 18, 2020 12:37 PM
>>>>>>>>>>>> To: [e-mail]
>>>>>>>>>>>> Subject: [EXTERNAL] [OAUTH-WG] OAuth 2.1: dropping password grant
>>>>>>>>>>>> 
>>>>>>>>>>>> Hey List 
>>>>>>>>>>>> 
>>>>>>>>>>>> (Once again using the OAuth 2.1 name as a placeholder for the doc that Aaron, Torsten, and I are working on)
>>>>>>>>>>>> 
>>>>>>>>>>>> In the security topics doc
>>>>>>>>>>>> 
>>>>>>>>>>>> https://tools.ietf.org/html/draft-ietf-oauth-security-topics-14#section-2.4
>>>>>>>>>>>> 
>>>>>>>>>>>> The password grant MUST not be used.
>>>>>>>>>>>> 
>>>>>>>>>>>> Some background for those interested. I added this grant into OAuth 2.0 to allow applications that had been provided password to migrate. Even with the caveats in OAuth 2.0, implementors decide they want to prompt the user to enter their credentials, the anti-pattern OAuth was created to eliminate. 
>>>>>>>>>>>> 
>>>>>>>>>>>> 
>>>>>>>>>>>> Does anyone have concerns with dropping the password grant from the OAuth 2.1 document so that developers don't use it?
>>>>>>>>>>>> 
>>>>>>>>>>>> /Dick
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>>>>>>>>>>> -- 
>>>>>>>>>>> ----
>>>>>>>>>>> Aaron Parecki
>>>>>>>>>>> aaronparecki.com
>>>>>>>>>>> @aaronpk
>>>>>>>>>>> 
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