Extend payload

[loafoe]

Preflight Checklist

• [X] I agree to follow the Code of Conduct that this project adheres to.
• [X] I have searched the issue tracker for an issue that matches the one I want to file, without success.

Problem Description

Dex has very rigid claims support. Adding additional claims via a connector requires forking the code and making changes to various internal structures. There are a number of proposals where this discussed, namely https://github.com/dexidp/dex/issues/1635 . The scope of these is fairly large and we are exploring a possible solution that limits itself to just mutating of the claims.

Proposed Solution

We propose adding a new PayloadExtender interface which connectors can choose to implement:

// PayloadExtender allows connectors to enhance the payload before signing
type PayloadExtender interface {
	ExtendPayload(scopes []string, payload []byte, connectorData []byte) ([]byte, error)
}

By implementing this interface connectors get a chance to mutate the id_token payload just before it is signed. The scopes may be used to perform conditional mutation. The payload is passed as a byte array as well as the connectorData associated with the authorization request. This allows the connector to pass context via connectorData. The resulting mutated structure is returned including an error condition.

A working example of this interface implementation could look like this (actual working code):

func (c *hsdpConnector) ExtendPayload(scopes []string, payload []byte, cdata []byte) ([]byte, error) {
	var cd connectorData
	var originalClaims map[string]interface{}

	c.logger.Info("ExtendPayload called")

	if err := json.Unmarshal(cdata, &cd); err != nil {
		return payload, err
	}
	if err := json.Unmarshal(payload, &originalClaims); err != nil {
		return payload, err
	}
	
	// Experimental teams
	var teams []string
	teams = append(teams, cd.Introspect.Organizations.ManagingOrganization)
	originalClaims["teams"] = teams

	extendedPayload, err := json.Marshal(originalClaims)
	if err != nil {
		return payload, err
	}
	return extendedPayload, nil
}

This results in a teams claim being available in the id_token. A working implementation can be found in this fork.

Alternatives Considered

Alternatives are to maintain a fork with these changes.

Additional Information

There are only minimal (non-breaking) changes required to the core dex to support this, essentially changes to propagate the connectorData to the token generation logic. We have successfully tested this approach. If this is interesting I'm happy to write a Dex Feature Proposal which further details.

[sagikazarmark]

Thank you for opening this @loafoe!

Indeed a solution with a smaller scope may be easier to incorporate into Dex, but as part of the external connector effort (#1907) the connector interface maybe redesigned and this feature maybe replaced with something else (eg. middleware).

In any case, this proposal is worth exploring.

Would you mind opening an enhancement proposal?

I also wonder if it would make sense at this point to introduce an internal representation for the payload. That could serve as a basis for future improvements, like custom claims.

[loafoe]

Hi @sagikazarmark sorry for the delay. Just submitted a PR https://github.com/dexidp/dex/pull/2954 for the initial draft of the proposal. Feedback appreciated!

[kromanow94]

It'd be great to have that!