emissary/internal/auth/middleware.go

package auth

import (
	"context"
	"net/http"

	"github.com/pkg/errors"
	"gitlab.com/wpetit/goweb/api"
	"gitlab.com/wpetit/goweb/logger"
)

const (
	ErrCodeUnauthorized api.ErrorCode = "unauthorized"
	ErrCodeForbidden    api.ErrorCode = "forbidden"
)

type contextKey string

const (
	contextKeyUser contextKey = "user"
)

func CtxUser(ctx context.Context) (*User, error) {
	user, ok := ctx.Value(contextKeyUser).(*User)
	if !ok {
		return nil, errors.Errorf("unexpected user type: expected '%T', got '%T'", new(User), ctx.Value(contextKeyUser))
	}

	return user, nil
}

var ErrUnauthenticated = errors.New("unauthenticated")

type User interface {
	Subject() string
}

type Authenticator interface {
	Authenticate(context.Context, *http.Request) (User, error)
}

func Middleware(authenticators ...Authenticator) func(http.Handler) http.Handler {
	return func(h http.Handler) http.Handler {
		fn := func(w http.ResponseWriter, r *http.Request) {
			ctx := logger.With(r.Context(), logger.F("remoteAddr", r.RemoteAddr))

			var (
				user User
				err  error
			)

			for _, auth := range authenticators {
				user, err = auth.Authenticate(ctx, r)
				if err != nil {
					logger.Debug(ctx, "could not authenticate request", logger.E(errors.WithStack(err)))

					continue
				}

				if user != nil {
					break
				}
			}

			if user == nil {
				api.ErrorResponse(w, http.StatusUnauthorized, ErrCodeUnauthorized, nil)

				return
			}

			ctx = logger.With(ctx, logger.F("user", user.Subject()))
			ctx = context.WithValue(ctx, contextKeyUser, user)

			h.ServeHTTP(w, r.WithContext(ctx))
		}

		return http.HandlerFunc(fn)
	}
}