83 lines
3.8 KiB
Markdown
83 lines
3.8 KiB
Markdown
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# Proposal: design for revoking refresh tokens.
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Refresh tokens are issued to the client by the authorization server and are used
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to request a new access token when the current access token becomes invalid or expires.
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It is a common usecase for the end users to revoke client access to their identity.
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This proposal defines the changes needed in Dex v2 to support refresh token revocation.
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## Motivation
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1. Currently refresh tokens are not associated with the user. Need a new "session object" for this.
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2. Need an API to list refresh tokens based on the UserID.
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3. We need a way for users to login to dex and revoke a client.
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4. Limit the number refresh tokens for each user-client pair to 1.
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## Details
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Currently in Dex when an end user successfully logs in via a connector and has the OfflineAccess
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scope set to true, a refresh token is created and stored in the backing datastore. There is no
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association between the end user and the refresh token. Hence if we want to support the functionality
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of users being able to revoke refresh tokens, the first step is to have a structure in place that allows
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us retrieve a list of refresh tokens depending on the authenticated user.
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```go
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// Reference object for RefreshToken containing only metadata.
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type RefreshTokenRef struct {
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// ID of the RefreshToken
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ID string
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CreatedAt time.Time
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LastUsed time.Time
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}
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// Session objects pertaining to users with refresh tokens.
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//
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// Will have to handle garbage collection i.e. if no refresh token exists for a user,
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// this object must be cleaned up.
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type OfflineSession struct {
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// UserID of an end user who has logged in to the server.
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UserID string
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// The ID of the connector used to login the user.
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ConnID string
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// List of pointers to RefreshTokens issued for SessionID
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Refresh []*RefreshTokenRef
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}
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// Retrieve OfflineSession obj for given userId and connID
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func getOfflineSession (userId string, connID string)
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```
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### Changes in Dex CodeFlows
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1. Client requests a refresh token:
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Try to retrieve the `OfflineSession` object for the User with the given `UserID + ConnID`.
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This leads to two possibilities:
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* Object exists: This means a Refresh token already exists for the user.
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Update the existing `OffilineSession` object with the newly received token as follows:
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* CreateRefresh() will create a new `RefreshToken` obj in the storage.
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* Update the `Refresh` list with the new `RefreshToken` pointer.
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* Delete the old refresh token in storage.
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* No object found: This implies that this will be the first refresh token for the user.
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* CreateRefresh() will create a new `RefreshToken` obj in the storage.
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* Create an OfflineSession for the user and add the new `RefreshToken` pointer to
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the `Refresh` list.
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2. Refresh token rotation:
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There will be no change to this codeflow. When the client refreshes a refresh token, the `TokenID`
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still remains intact and only the `RefreshToken` obj gets updated with a new nonce. We do not need
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any additional checks in the OfflineSession objects as the `RefreshToken` pointers still remain intact.
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3. User revokes a refresh token (New functionality):
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A user that has been authenticated externally will have the ability to revoke their refresh tokens.
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Please note that Dex's API does not perform the authentication, this will have to be done by an
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external app.
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Steps involved:
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* Get `OfflineSession` obj with given UserID + ConnID.
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* If a refresh token exists in `Refresh`, delete the `RefreshToken` (handle this in storage)
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and its pointer value in `Refresh`. Clean up the OfflineSession object.
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* If there is no refresh token found, handle error case.
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NOTE: To avoid race conditions between “requesting a refresh token” and “revoking a refresh token”, use
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locking mechanism when updating an `OfflineSession` object.
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