provider.go

package oidc

import (
	"context"
	"errors"
	"fmt"
	"net/http"
	"strings"

	gooidc "github.com/coreos/go-oidc/v3/oidc"
	log "github.com/sirupsen/logrus"
	"golang.org/x/oauth2"

	"github.com/argoproj/argo-cd/v2/util/security"
	"github.com/argoproj/argo-cd/v2/util/settings"
)

// Provider is a wrapper around go-oidc provider to also provide the following features:
// 1. lazy initialization/querying of the provider
// 2. automatic detection of change in signing keys
// 3. convenience function for verifying tokens
// We have to initialize the provider lazily since Argo CD can be an OIDC client to itself (in the
// case of dex reverse proxy), which presents a chicken-and-egg problem of (1) serving dex over
// HTTP, and (2) querying the OIDC provider (ourself) to initialize the OIDC client.
type Provider interface {
	Endpoint() (*oauth2.Endpoint, error)

	ParseConfig() (*OIDCConfiguration, error)

	Verify(tokenString string, argoSettings *settings.ArgoCDSettings) (*gooidc.IDToken, error)
}

type providerImpl struct {
	issuerURL      string
	client         *http.Client
	goOIDCProvider *gooidc.Provider
}

var _ Provider = &providerImpl{}

// NewOIDCProvider initializes an OIDC provider
func NewOIDCProvider(issuerURL string, client *http.Client) Provider {
	return &providerImpl{
		issuerURL: issuerURL,
		client:    client,
	}
}

// oidcProvider lazily initializes, memoizes, and returns the OIDC provider.
func (p *providerImpl) provider() (*gooidc.Provider, error) {
	if p.goOIDCProvider != nil {
		return p.goOIDCProvider, nil
	}
	prov, err := p.newGoOIDCProvider()
	if err != nil {
		return nil, err
	}
	p.goOIDCProvider = prov
	return p.goOIDCProvider, nil
}

// newGoOIDCProvider creates a new instance of go-oidc.Provider querying the well known oidc
// configuration path (http://example-argocd.com/api/dex/.well-known/openid-configuration)
func (p *providerImpl) newGoOIDCProvider() (*gooidc.Provider, error) {
	log.Infof("Initializing OIDC provider (issuer: %s)", p.issuerURL)
	ctx := gooidc.ClientContext(context.Background(), p.client)
	prov, err := gooidc.NewProvider(ctx, p.issuerURL)
	if err != nil {
		return nil, fmt.Errorf("Failed to query provider %q: %v", p.issuerURL, err)
	}
	s, _ := ParseConfig(prov)
	log.Infof("OIDC supported scopes: %v", s.ScopesSupported)
	return prov, nil
}

type tokenVerificationError struct {
	errorsByAudience map[string]error
}

func (t tokenVerificationError) Error() string {
	var errorStrings []string
	for aud, err := range t.errorsByAudience {
		errorStrings = append(errorStrings, fmt.Sprintf("error for aud %q: %v", aud, err))
	}
	return fmt.Sprintf("token verification failed for all audiences: %s", strings.Join(errorStrings, ", "))
}

func (p *providerImpl) Verify(tokenString string, argoSettings *settings.ArgoCDSettings) (*gooidc.IDToken, error) {
	// According to the JWT spec, the aud claim is optional. The spec also says (emphasis mine):
	//
	//   If the principal processing the claim does not identify itself with a value in the "aud" claim _when this
	//   claim is present_, then the JWT MUST be rejected.
	//
	//     - https://www.rfc-editor.org/rfc/rfc7519#section-4.1.3
	//
	// If the claim is not present, we can skip the audience claim check (called the "ClientID check" in go-oidc's
	// terminology).
	//
	// The OIDC spec says that the aud claim is required (https://openid.net/specs/openid-connect-core-1_0.html#IDToken).
	// But we cannot assume that all OIDC providers will follow the spec. For Argo CD <2.6.0, we will default to
	// allowing the aud claim to be optional. In Argo CD >=2.6.0, we will default to requiring the aud claim to be
	// present and give users the skipAudienceCheckWhenTokenHasNoAudience setting to revert the behavior if necessary.
	//
	// At this point, we have not verified that the token has not been altered. All code paths below MUST VERIFY
	// THE TOKEN SIGNATURE to confirm that an attacker did not maliciously remove the "aud" claim.
	unverifiedHasAudClaim, err := security.UnverifiedHasAudClaim(tokenString)
	if err != nil {
		return nil, fmt.Errorf("failed to determine whether the token has an aud claim: %w", err)
	}

	var idToken *gooidc.IDToken
	if !unverifiedHasAudClaim {
		idToken, err = p.verify("", tokenString, argoSettings.SkipAudienceCheckWhenTokenHasNoAudience())
	} else {
		allowedAudiences := argoSettings.OAuth2AllowedAudiences()
		if len(allowedAudiences) == 0 {
			return nil, errors.New("token has an audience claim, but no allowed audiences are configured")
		}
		tokenVerificationErrors := make(map[string]error)
		// Token must be verified for at least one allowed audience
		for _, aud := range allowedAudiences {
			idToken, err = p.verify(aud, tokenString, false)
			tokenExpiredError := &gooidc.TokenExpiredError{}
			if errors.As(err, &tokenExpiredError) {
				// If the token is expired, we won't bother checking other audiences. It's important to return a
				// TokenExpiredError instead of an error related to an incorrect audience, because the caller may
				// have specific behavior to handle expired tokens.
				break
			}
			if err == nil {
				break
			}
			// We store the error for each audience so that we can return a more detailed error message to the user.
			// If this gets merged, we'll be able to detect failures unrelated to audiences and short-circuit this loop
			// to avoid logging irrelevant warnings: https://github.com/coreos/go-oidc/pull/406
			tokenVerificationErrors[aud] = err
		}
		// If the most recent attempt encountered an error, and if we have collected multiple errors, switch to the
		// other error type to gather more context.
		if err != nil && len(tokenVerificationErrors) > 0 {
			err = tokenVerificationError{errorsByAudience: tokenVerificationErrors}
		}
	}

	if err != nil {
		return nil, fmt.Errorf("failed to verify token: %w", err)
	}

	return idToken, nil
}

func (p *providerImpl) verify(clientID, tokenString string, skipClientIDCheck bool) (*gooidc.IDToken, error) {
	ctx := context.Background()
	prov, err := p.provider()
	if err != nil {
		return nil, err
	}
	config := &gooidc.Config{ClientID: clientID, SkipClientIDCheck: skipClientIDCheck}
	verifier := prov.Verifier(config)
	idToken, err := verifier.Verify(ctx, tokenString)
	if err != nil {
		// HACK: if we failed token verification, it's possible the reason was because dex
		// restarted and has new JWKS signing keys (we do not back dex with persistent storage
		// so keys might be regenerated). Detect this by:
		// 1. looking for the specific error message
		// 2. re-initializing the OIDC provider
		// 3. re-attempting token verification
		// NOTE: the error message is sensitive to implementation of verifier.Verify()
		if !strings.Contains(err.Error(), "failed to verify signature") {
			return nil, err
		}
		newProvider, retryErr := p.newGoOIDCProvider()
		if retryErr != nil {
			// return original error if we fail to re-initialize OIDC
			return nil, err
		}
		verifier = newProvider.Verifier(config)
		idToken, err = verifier.Verify(ctx, tokenString)
		if err != nil {
			return nil, err
		}
		// If we get here, we successfully re-initialized OIDC and after re-initialization,
		// the token is now valid.
		log.Info("New OIDC settings detected")
		p.goOIDCProvider = newProvider
	}
	return idToken, nil
}

func (p *providerImpl) Endpoint() (*oauth2.Endpoint, error) {
	prov, err := p.provider()
	if err != nil {
		return nil, err
	}
	endpoint := prov.Endpoint()
	return &endpoint, nil
}

// ParseConfig parses the OIDC Config into the concrete datastructure
func (p *providerImpl) ParseConfig() (*OIDCConfiguration, error) {
	prov, err := p.provider()
	if err != nil {
		return nil, err
	}
	return ParseConfig(prov)
}

// ParseConfig parses the OIDC Config into the concrete datastructure
func ParseConfig(provider *gooidc.Provider) (*OIDCConfiguration, error) {
	var conf OIDCConfiguration
	err := provider.Claims(&conf)
	if err != nil {
		return nil, err
	}
	return &conf, nil
}