165 lines
6.4 KiB
Markdown
165 lines
6.4 KiB
Markdown
# Proposal: upstream refreshing
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## TL;DR
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Today, if a user deletes their GitHub account, dex will keep allowing clients to
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refresh tokens on that user's behalf because dex never checks back in with
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GitHub.
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This is a proposal to change the connector package so the dex can check back
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in with GitHub.
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## The problem
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When dex is federating to an upstream identity provider (IDP), we want to ensure
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claims being passed onto clients remain fresh. This includes data such as Google
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accounts display names, LDAP group membership, account deactivations. Changes to
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these on an upstream IDP should always be reflected in the claims dex passes to
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its own clients.
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Refresh tokens make this complicated. When refreshing a token, unlike normal
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logins, dex doesn't have the opportunity to prompt for user interaction. For
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example, if dex is proxying to a LDAP server, it won't have the user's username
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and passwords.
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Dex can't do this today because connectors have no concept of checking back in
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with an upstream provider (with the sole exception of groups). They're only
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called during the initial login, and never consulted when dex needs to mint a
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new refresh token for a client. Additionally, connectors aren't actually aware
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of the scopes being requested by the client, so they don't know when they should
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setup the ability to check back in and have to treat every request identically.
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## Changes to the connector package
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The biggest changes proposed impact the connector package and connector
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implementations.
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1. Connectors should be consulted when dex attempts to refresh a token.
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2. Connectors should be aware of the scopes requested by the client.
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The second bullet is important because of the first. If a client isn't
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requesting a refresh token, the connector shouldn't do the extra work, such as
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requesting additional upstream scopes.
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to address the first point, a top level `Scopes` object will be added to the
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connector package to express the scopes requested by the client. The
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`CallbackConnector` and `PasswordConnector` will be updated accordingly.
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```go
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// Scopes represents additional data requested by the clients about the end user.
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type Scopes struct{
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// The client has requested a refresh token from the server.
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OfflineAccess bool
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// The client has requested group information about the end user.
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Groups bool
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}
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// CallbackConnector is an interface implemented by connectors which use an OAuth
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// style redirect flow to determine user information.
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type CallbackConnector interface {
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// The initial URL to redirect the user to.
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//
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// OAuth2 implementations should request different scopes from the upstream
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// identity provider based on the scopes requested by the downstream client.
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// For example, if the downstream client requests a refresh token from the
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// server, the connector should also request a token from the provider.
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LoginURL(s Scopes, callbackURL, state string) (string, error)
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// Handle the callback to the server and return an identity.
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HandleCallback(s Scopes, r *http.Request) (identity Identity, state string, err error)
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}
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// PasswordConnector is an interface implemented by connectors which take a
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// username and password.
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type PasswordConnector interface {
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Login(s Scopes, username, password string) (identity Identity, validPassword bool, err error)
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}
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```
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The existing `GroupsConnector` plays two roles.
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1. The connector only attempts to grab groups when the downstream client requests it.
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2. Allow group information to be refreshed.
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The first issue is remedied by the added `Scopes` struct. This proposal also
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hopes to generalize the need of the second role by adding a more general
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`RefreshConnector`:
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```go
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type Identity struct {
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// Existing fields...
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// Groups are added to the identity object, since connectors are now told
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// if they're being requested.
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// The set of groups a user is a member of.
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Groups []string
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}
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// RefreshConnector is a connector that can update the client claims.
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type RefreshConnector interface {
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// Refresh is called when a client attempts to claim a refresh token. The
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// connector should attempt to update the identity object to reflect any
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// changes since the token was last refreshed.
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Refresh(s Scopes, identity Identity) (Identity, error)
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// TODO(ericchiang): Should we allow connectors to indicate that the user has
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// been delete or an upstream token has been revoked? This would allow us to
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// know when we should remove the downstream refresh token, and when there was
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// just a server error, but might be hard to determine for certain protocols.
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// Might be safer to always delete the downstream token if the Refresh()
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// method returns an error.
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}
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```
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## Example changes to the "passwordDB" connector
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The `passwordDB` connector is the internal connector maintained by the server.
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As an example, these are the changes to that connector if this change was
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accepted.
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```go
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func (db passwordDB) Login(s connector.Scopes, username, password string) (connector.Identity, bool, error) {
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// No change to existing implementation. Scopes can be ignored since we'll
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// always have access to the password objects.
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}
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func (db passwordDB) Refresh(s connector.Scopes, identity connector.Identity) (connector.Identity, error) {
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// If the user has been deleted, the refresh token will be rejected.
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p, err := db.s.GetPassword(identity.Email)
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if err != nil {
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if err == storage.ErrNotFound {
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return connector.Identity{}, errors.New("user not found")
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}
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return connector.Identity{}, fmt.Errorf("get password: %v", err)
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}
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// User removed but a new user with the same email exists.
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if p.UserID != identity.UserID {
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return connector.Identity{}, errors.New("user not found")
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}
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// If a user has updated their username, that will be reflected in the
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// refreshed token.
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identity.Username = p.Username
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return identity, nil
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}
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```
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## Caveats
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Certain providers, such as Google, will only grant a single refresh token for each
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client + end user pair. The second time one's requested, no refresh token is
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returned. This means refresh tokens must be stored by dex as objects on an
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upstream identity rather than part of a downstream refresh even.
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Right now `ConnectorData` is too general for this since it is only stored with a
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refresh token and can't be shared between sessions. This should be rethought in
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combination with the [`user-object.md`](./user-object.md) proposal to see if
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there are reasonable ways for us to do this.
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This isn't a problem for providers like GitHub because they return the same
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refresh token every time. We don't need to track a token per client.
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