fix: requested scope ignored in refresh flow #718

james-d-elliott · 2022-11-02T09:17:22Z

This addresses an issue where the clients requested scope is ignored during the refresh flow preventing a refresh token from granting an access token with a more narrow scope. It is critical to note that it is completely ignored, and previous behaviour only issued the same scope as originally granted. An access request which requests a broader scope is equally ignored and it has been thoroughly tested to ensure this cannot occur in HEAD. See https://www.rfc-editor.org/rfc/rfc6749#section-6 for more information.

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I have read the contributing guidelines and signed the CLA.
I have referenced an issue containing the design document if my change introduces a new feature.
I have read the security policy.
I confirm that this pull request does not address a security vulnerability.
If this pull request addresses a security vulnerability,
I confirm that I got approval (please contact security@ory.sh) from the maintainers to push the changes.
I have added tests that prove my fix is effective or that my feature works.
I have added the necessary documentation within the code base (if appropriate).

Further comments

james-d-elliott

I've done a self review to highlight sections that I am unsure on and to give some context to the changes.

handler/oauth2/flow_refresh.go

aeneasr

This looks very good! Just one minor question

handler/oauth2/flow_refresh.go

james-d-elliott · 2022-11-03T19:29:54Z

Regaring the following sequence;

Request token with scope a,b,c
Do refresh token with scope a,b
Do refresh token with scope a,b,c

I can confirm with my high level testing that it fails at step 3.

james-d-elliott · 2022-11-03T22:15:14Z

So looking here:

fosite/handler/oauth2/flow_refresh.go

Line 64 in cda9c24

    
           originalRequest, err := c.TokenRevocationStorage.GetRefreshTokenSession(ctx, signature, request.GetSession())

The original request we're looking up is the RT Session. Thus I think IF we want to preserve the original scope we just have to ensure the new RT session has the same scope as the original (granted), and the AT session has the narrowed scope. We just have to decide if that's desirable. With the current code including that addition would result in a second refresh without the scope value to restore the initially granted scope, and with the value the RP would be able to obtain the original scopes again or any subset of them even if they are not the same subset as the first refresh. See the flow sequences below.

The issue is I'm not entirely sure how we'd accomplish that, looking at the code it looks like the RT session and AT sessions share their scope. Maybe we have to have a new value to store the scope specific to the RT session, which defaults to the scope of the AT session so that it's appropriately handled during the PopulateTokenEndpointResponse.

If we did add this functionality the following flow sequence would be accurate (with a client which is authorized to grant scope openid foo bar baz fizz offline_access):

Relying party requests access to a completely new token with scope openid foo bar baz offline_access
1. Relying party is granted scope openid foo bar baz
Relying party requests access to a refresh without a scope
1. Relying party is granted scope openid foo bar baz
Relying party requests access to a refresh with a scope of openid foo bar
1. Relying party is granted scope openid foo bar
Relying party requests access to a refresh with a scope of openid bar baz
1. Relying party is granted scope openid bar baz
Relying party requests access to a refresh without a scope
1. Relying party is granted scope openid foo bar baz
Relying party requests access to a refresh with a scope of openid foo bar baz fizz
1. Relying party is rejected invalid_scope because they were not granted this scope in step 1
Relying party requests access to a completely new token with scope openid fizz buzz offline_access
1. Relying party is rejected invalid_scope because the client is not permitted to request a scope with buzz

aeneasr · 2022-11-04T06:46:40Z

The original request we're looking up is the RT Session. Thus I think IF we want to preserve the original scope we just have to ensure the new RT session has the same scope as the original (granted), and the AT session has the narrowed scope.

To me that sounds very, very reasonable!

james-d-elliott · 2022-11-04T07:45:23Z

@aeneasr I'm fairly sure of the most effective way to achieve this, however you probably know this code base better than anyone so maybe I've missed something or you have an alternative way that is preferable.

This is the critical path in making this functional I believe:

fosite/handler/oauth2/flow_refresh.go

Lines 190 to 199 in cda9c24

    
           storeReq := requester.Sanitize([]string{}) 
        
           storeReq.SetID(ts.GetID()) 
        
           if err = c.TokenRevocationStorage.CreateAccessTokenSession(ctx, accessSignature, storeReq); err != nil { 
        
           	return err 
        
           } 
        
           if err = c.TokenRevocationStorage.CreateRefreshTokenSession(ctx, refreshSignature, storeReq); err != nil { 
        
           	return err 
        
           }

We need to ensure the storeReq for the AT contains the narrowed scope and that the storeReq for the RT contains the original scope I believe.

I think the best way to achieve this is to add an interface which extends AccessRequester with the following signature:

// RefreshTokenAccessRequester is an extended AccessRequester implementation that allows preserving
// the original scopes between refresh access requests allowing an relying-party to narrow the scope of
// the access token and then broaden them again to the resource owners original grant.
type RefreshTokenAccessRequester interface {
	// GetRefreshTokenRequestedScopes returns the request's scopes specifically for the refresh token.
	GetRefreshTokenRequestedScopes() (scopes Arguments)
	// SetRefreshTokenRequestedScopes sets the request's scopes specifically for the refresh token.
	SetRefreshTokenRequestedScopes(scopes Arguments)
	// GetRefreshTokenGrantedScopes returns all granted scopes specifically for the refresh token.
	GetRefreshTokenGrantedScopes() (grantedScopes Arguments)
	// SetRefreshTokenRequestedScopes sets the request's scopes specifically for the refresh token.
	SetRefreshTokenRequestedScopes(scopes Arguments)
	
	AccessRequester
}

The key thing being that if that interface is not implemented that people would not have this functionality.

aeneasr · 2022-11-04T07:50:41Z

I think that could work! We probably need a few more tests to ensure that this works without getting confused in the process in longer refresh token chains :)

access_request.go

aeneasr

Awesome, getting much closer! :)

handler/oauth2/flow_refresh.go

access_request.go

vivshankar

@james-d-elliott Thanks for this PR! I had a couple of observations that you might consider.

vivshankar · 2023-07-07T03:25:59Z

handler/oauth2/flow_refresh.go

-	if err = c.TokenRevocationStorage.CreateRefreshTokenSession(ctx, refreshSignature, storeReq); err != nil {
-		return err
+	if rtRequest, ok := requester.(fosite.RefreshTokenAccessRequester); ok {
+		rtStoreReq := requester.Sanitize([]string{}).(*fosite.Request)


@james-d-elliott Wondering if this negates the idea of having a Requester interface at all. I understand why you do it though.

A better approach might be to introduce an interface that allows you to invoke SetGrantedScopes and SetRequestedScopes?

Yeah, the only intent behind this was to avoid breaking any other implementation. I'm completely fine with which ever approach most fits with how ory is using this however.

In the spirit of preserving the interfaces, I suggest a new interface be added that is able to mutate scopes in the requester.

This has been addressed in a use specific way I believe.

handler/oauth2/flow_refresh.go

This addresses an issue where the clients requested scope is ignored during the refresh flow preventing a refresh token from granting an access token with a more narrow scope. It is critical to note that it is completely ignored, and previous behaviour only issued the same scope as originally granted. An access request which requests a broader scope is equally ignored and it has been thoroughly tested to ensure this cannot occur in HEAD. See https://www.rfc-editor.org/rfc/rfc6749#section-6 for more information.

vivshankar

LGTM. Approving FWIW :-)

james-d-elliott

RFC. Also the intention behind them is bad clients which this change may cause breakage for as highlighted by Vivek.

james-d-elliott · 2023-07-21T05:57:02Z

handler/oauth2/flow_refresh.go

+	// IgnoreRequestedScopeNotInOriginalGrant determines the action to take when the requested scopes in the refresh
+	// flow were not originally granted. If false which is the default the handler will automatically return an error.
+	// If true the handler will filter out / ignore the scopes which were not originally granted.
+	IgnoreRequestedScopeNotInOriginalGrant bool


Side note when looking at this. I have a per-client implementation of this utilizing an interface which passes the same tests. Maybe this is more desirable?

Why is this not made through a new config interface?

To me it looks like currently all config is done through config interface, even if it is not meant for hot reloading?

james-d-elliott · 2023-07-21T05:57:15Z

handler/oauth2/flow_refresh.go

+			if c.IgnoreRequestedScopeNotInOriginalGrant {
+				// Skips addressing point 2 of the text in RFC6749 Section 6 and instead just prevents the scope
+				// requested from being granted.
+				continue
+			} else {
+				// Addresses point 2 of the text in RFC6749 Section 6.
+				return errorsx.WithStack(fosite.ErrInvalidScope.WithHintf("The requested scope '%s' was not originally granted by the resource owner.", scope))
+			}


Side note when looking at this. I have a per-client implementation of this utilizing an interface which passes the same tests. Maybe this is more desirable?

What would be the use case of having this per-client?

The only way I'll personally use it is per-client where the default is to enforce the spec and you make an exception on a per-client basis. I'm happy enough to maintain my own entire implementation however.

mitar · 2024-02-15T08:24:23Z

handler/oauth2/flow_refresh.go

-	if err = c.TokenRevocationStorage.CreateRefreshTokenSession(ctx, refreshSignature, storeReq); err != nil {
-		return err
+	if rtRequest, ok := requester.(fosite.RefreshTokenAccessRequester); ok {
+		rtStoreReq := rtRequest.SanitizeRestoreRefreshTokenOriginalRequester(originalRequest)


What is this change about? Why it is necessary?

Because the scopes of the current request are for the access token, not the refresh token. The scopes of the original granted refresh token must be restored to make it possible to meet the strict requirements of the spec:

If a new refresh token is issued, the refresh token scope MUST be identical to that of the refresh token included by the client in the request.

No, I mean, my question is why you have two cases here. It looks like you added RefreshTokenAccessRequester for backwards compatibility? But it feels to me that if you do not implement RefreshTokenAccessRequester then you get wrong behavior? Not sure if we should keep the old behavior at all?

Also, I am not sure that an extra method is already needed here? Sanitize returns a clone of requester to begin with? And you then call just:

ar.SetID(requester.GetID()) ar.SetRequestedScopes(requester.GetRequestedScopes()) ar.SetGrantedScopes(requester.GetGrantedScopes())

So why not just call originalRequest.Sanitize(nil) and then those three calls above, here, at this point? Without a method?

Probably I am missing something, I just checked very quickly this.

An AccessRequester doesn't have SetGranted* receivers as part of the implementation. So a new receiver will be needed regardless. The question is just about what solution is going to lead to the least harmful outcome.

Adding those receivers to the AccessRequester interface seems like a poor choice as it isn't used now but could potentially lead to implementers making harmful decisions in this stage of the relevant flows in my opinion.

As far as the other I brought it up with aeneasr I believe so really up to an ory preference (he may have actually asked for it but I don't recall specifics). I personally don't have one myself in either direction.

It has GrantScope? Isn't this enough? You loop over all granted scopes and call GrantScope?

I see the same being done currently in the code:

request.SetID(originalRequest.GetID()) request.SetSession(originalRequest.GetSession().Clone()) request.SetRequestedScopes(originalRequest.GetRequestedScopes()) request.SetRequestedAudience(originalRequest.GetRequestedAudience()) for _, scope := range originalRequest.GetGrantedScopes() { if !c.Config.GetScopeStrategy(ctx)(request.GetClient().GetScopes(), scope) { return errorsx.WithStack(fosite.ErrInvalidScope.WithHintf("The OAuth 2.0 Client is not allowed to request scope '%s'.", scope)) } request.GrantScope(scope) } ... for _, audience := range originalRequest.GetGrantedAudience() { request.GrantAudience(audience) }

I see this was a previous comment here: #718 (comment)

So to seems there is already some code to clone a requester. Maybe that should be just moved out into utility function and reused here for refresh token as well?

(And again sorry if I am missing something.)

james-d-elliott requested a review from aeneasr as a code owner November 2, 2022 09:17

james-d-elliott commented Nov 2, 2022

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james-d-elliott changed the title ~~fix(oauth2): requested scope ignored in refresh flow~~ fix: requested scope ignored in refresh flow Nov 2, 2022

james-d-elliott force-pushed the fix-refresh-scope-narrowing branch from 5eb68a9 to f35f7d0 Compare November 2, 2022 09:33

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james-d-elliott mentioned this pull request Jan 2, 2023

fix: fosite refresh scope narrowing e2e ory/hydra#3403

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james-d-elliott added 5 commits July 21, 2023 09:37

fix: retain refresh_token original scopes

5d4da29

test: add integration test

c5c6056

refactor: remove unnecessary receiver

deb3be3

refactor: simplify logic

6db02e8

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feat: filtering mode

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vivshankar mentioned this pull request Aug 26, 2023

fix: requested scope ignored in refresh flow vivshankar/fosite#5

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james-d-elliott added 2 commits September 4, 2023 18:48

fix: exact scope only during refresh original comparison

9a0bc79

Merge branch 'master' into fix-refresh-scope-narrowing

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fix: requested scope ignored in refresh flow #718

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james-d-elliott commented Nov 2, 2022

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