auth/authmw/token.go

package authmw

import (
	"context"
	"crypto/x509"
	"encoding/json"
	"fmt"
	"net/http"
	"slices"
	"strings"

	"git.t-juice.club/microfilm/auth"
	"github.com/golang-jwt/jwt/v5"
)

func VerifyToken(authURL string, permittedRoles []string) func(http.Handler) http.Handler {
	// Fetch current pubkey
	url := fmt.Sprintf("%s/key", authURL)
	req, err := http.NewRequest(http.MethodGet, url, nil)
	if err != nil {
		panic(err)
	}

	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		panic(err)
	}
	defer resp.Body.Close()

	var authResponse auth.PubkeyResponse
	decoder := json.NewDecoder(resp.Body)
	if err := decoder.Decode(&authResponse); err != nil {
		panic(err)
	}

	// Parse pubkey
	pub, err := x509.ParsePKIXPublicKey(authResponse.PubKey)
	if err != nil {
		panic(err)
	}

	fn := func(next http.Handler) http.Handler {
		fn := func(w http.ResponseWriter, r *http.Request) {
			authHeader := r.Header.Get("Authorization")
			if !strings.Contains(authHeader, "Bearer ") {
				// No token, pass if unathorized in permitted
				// else reject
				if slices.Contains[[]string, string](permittedRoles, auth.RoleUnauthorized) {
					next.ServeHTTP(w, r)
					return
				}

				// Reject and write error response
				w.WriteHeader(http.StatusUnauthorized)
				var errResp auth.ErrorResponse
				errResp.Message = fmt.Sprintf("Authorization required: %s", strings.Join(permittedRoles, ","))
				errResp.Status = http.StatusUnauthorized

				encoder := json.NewEncoder(w)
				_ = encoder.Encode(&errResp)
				return
			}

			// Validate token
			tokenString := strings.Split(authHeader, " ")[1]
			token, err := jwt.ParseWithClaims(tokenString, &auth.MicrofilmClaims{}, func(t *jwt.Token) (interface{}, error) { return pub, nil })
			if err != nil {
				// Reject and write error response
				w.WriteHeader(http.StatusUnauthorized)
				var errResp auth.ErrorResponse
				errResp.Message = fmt.Sprintf("Token verification failed: %s", err)
				errResp.Status = http.StatusUnauthorized

				encoder := json.NewEncoder(w)
				_ = encoder.Encode(&errResp)
				return
			}

			// Add claims to request context
			if claims, ok := token.Claims.(*auth.MicrofilmClaims); ok && token.Valid {
				ctx := context.WithValue(r.Context(), "claims", claims)
				next.ServeHTTP(w, r.WithContext(ctx))
				return
			}

			next.ServeHTTP(w, r)
		}
		return http.HandlerFunc(fn)
	}

	return fn
}