Add option in oidc to hit the optional userinfo endpoint

Some oauth providers return "thin tokens" which won't include all of the
claims requested. This simply adds an option which will make the oidc
connector use the userinfo endpoint to fetch all the claims.

connector/oidc/oidc.go

@@ -39,6 +39,11 @@ type Config struct {
 
 	// Override the value of email_verifed to true in the returned claims
 	InsecureSkipEmailVerified bool `json:"insecureSkipEmailVerified"`
+
+	// GetUserInfo uses the userinfo endpoint to get additional claims for
+	// the token. This is especially useful where upstreams return "thin"
+	// id tokens
+	GetUserInfo bool `json:"getUserInfo"`
 }
 
 // Domains that don't support basic auth. golang.org/x/oauth2 has an internal
@@ -105,6 +110,7 @@ func (c *Config) Open(id string, logger log.Logger) (conn connector.Connector, e
 
 	clientID := c.ClientID
 	return &oidcConnector{
+		provider:    provider,
 		redirectURI: c.RedirectURI,
 		oauth2Config: &oauth2.Config{
 			ClientID:     clientID,
@@ -120,6 +126,7 @@ func (c *Config) Open(id string, logger log.Logger) (conn connector.Connector, e
 		cancel:                    cancel,
 		hostedDomains:             c.HostedDomains,
 		insecureSkipEmailVerified: c.InsecureSkipEmailVerified,
+		getUserInfo:               c.GetUserInfo,
 	}, nil
 }
 
@@ -129,6 +136,7 @@ var (
 )
 
 type oidcConnector struct {
+	provider                  *oidc.Provider
 	redirectURI               string
 	oauth2Config              *oauth2.Config
 	verifier                  *oidc.IDTokenVerifier
@@ -137,6 +145,7 @@ type oidcConnector struct {
 	logger                    log.Logger
 	hostedDomains             []string
 	insecureSkipEmailVerified bool
+	getUserInfo               bool
 }
 
 func (c *oidcConnector) Close() error {
@@ -219,6 +228,16 @@ func (c *oidcConnector) HandleCallback(s connector.Scopes, r *http.Request) (ide
 
 	}
 
+	if c.getUserInfo {
+		userInfo, err := c.provider.UserInfo(r.Context(), oauth2.StaticTokenSource(token))
+		if err != nil {
+			return identity, fmt.Errorf("oidc: error loading userinfo: %v", err)
+		}
+		if err := userInfo.Claims(&claims); err != nil {
+			return identity, fmt.Errorf("oidc: failed to decode userinfo claims: %v", err)
+		}
+	}
+
 	identity = connector.Identity{
 		UserID:        idToken.Subject,
 		Username:      claims.Username,