No way to check if server supports UserInfo

[crawshaw]

The server's .well-known/openid-configuration reports a UserInfo endpoint which is used in the UserInfo method. If the OIDC provider does not report an endpoint, UserInfo reports an error. But there is no way programmatically check beforehand and no way to check the error message other than string matching:

ui, err = provider.UserInfo(ctx, source)
if !strings.Contains(err.Error(), "user info endpoint is not supported") {
        // handle it
}

It would be nice if it were possible to avoid string matching on the error. Perhaps either something to pass to errors.Is or a mechanism for inspecting the contents of the .well-known/openid-configuration that the package fetched?

[ericchiang]

Does something like the following work? (sorry, Claims is probably a bad name for "inspect the provider config")

https://pkg.go.dev/github.com/coreos/go-oidc/v3/oidc#Provider.Claims

package main

import (
	"context"
	"fmt"
	"log"

	"github.com/coreos/go-oidc/v3/oidc"
)

func main() {
	ctx := context.Background()
	p, err := oidc.NewProvider(ctx, "https://accounts.google.com")
	if err != nil {
		log.Fatalf("getting provider info: %v", err)
	}
	var claims struct {
		UserInfoEndpoint string `json:"userinfo_endpoint"`
	}
	if err := p.Claims(&claims); err != nil {
		log.Fatalf("parsing provider info: %v", err)
	}
	if claims.UserInfoEndpoint != "" {
		fmt.Println("userinfo_endpoint:", claims.UserInfoEndpoint)
	} else {
		fmt.Println("userinfo_endpoint not supported")
	}
}