The jwtauth http middleware package provides a simple way to verify a JWT token from a http request and send the result down the request context (context.Context).

Please note, jwtauth works with any Go http router, but resides under the go-chi group for maintenance and organization - its only 3rd party dependency is the underlying jwt library "github.com/lestrrat-go/jwx".

In a complete JWT-authentication flow, you'll first capture the token from a http request, decode it, verify it and then validate that its correctly signed and hasn't expired - the jwtauth.Verifier middleware handler takes care of all of that. The jwtauth.Verifier will set the context values on keys jwtauth.TokenCtxKey and jwtauth.ErrorCtxKey.

Next, it's up to an authentication handler to respond or continue processing after the jwtauth.Verifier. The jwtauth.Authenticator middleware responds with a 401 Unauthorized plain-text payload for all unverified tokens and passes the good ones through. You can also copy the Authenticator and customize it to handle invalid tokens to better fit your flow (ie. with a JSON error response body).

By default, the Verifier will search for a JWT token in a http request, in the order:

1. 'Authorization: BEARER T' request header
2. 'jwt' Cookie value

The first JWT string that is found as an authorization header or cookie header is then decoded by the lestrrat-go/jwx library and a jwt.Token object is set on the request context. In the case of a signature decoding error the Verifier will also set the error on the request context.

The Verifier always calls the next http handler in sequence, which can either be the generic jwtauth.Authenticator middleware or your own custom handler which checks the request context jwt token and error to prepare a custom http response.

Note: jwtauth supports custom verification sequences for finding a token from a request by using the Verify middleware instantiator directly. The default Verifier is instantiated by calling Verify(ja, TokenFromHeader, TokenFromCookie).

See the full example.

package main

import (
	"fmt"
	"net/http"

	"github.com/go-chi/chi/v5"
	"github.com/go-chi/jwtauth/v5"
)

var tokenAuth *jwtauth.JWTAuth

func init() {
	tokenAuth = jwtauth.New("HS256", []byte("secret"), nil)

	// For debugging/example purposes, we generate and print
	// a sample jwt token with claims `user_id:123` here:
	_, tokenString, _ := tokenAuth.Encode(map[string]interface{}{"user_id": 123})
	fmt.Printf("DEBUG: a sample jwt is %s\n\n", tokenString)
}

func main() {
	addr := ":3333"
	fmt.Printf("Starting server on %v\n", addr)
	http.ListenAndServe(addr, router())
}

func router() http.Handler {
	r := chi.NewRouter()

	// Protected routes
	r.Group(func(r chi.Router) {
		// Seek, verify and validate JWT tokens
		r.Use(jwtauth.Verifier(tokenAuth))

		// Handle valid / invalid tokens. In this example, we use
		// the provided authenticator middleware, but you can write your
		// own very easily, look at the Authenticator method in jwtauth.go
		// and tweak it, its not scary.
		r.Use(jwtauth.Authenticator(tokenAuth))

		r.Get("/admin", func(w http.ResponseWriter, r *http.Request) {
			_, claims, _ := jwtauth.FromContext(r.Context())
			w.Write([]byte(fmt.Sprintf("protected area. hi %v", claims["user_id"])))
		})
	})

	// Public routes
	r.Group(func(r chi.Router) {
		r.Get("/", func(w http.ResponseWriter, r *http.Request) {
			w.Write([]byte("welcome anonymous"))
		})
	})

	return r
}

See https://github.com/goware/jwtutil for utility to help you generate JWT tokens.

go install github.com/goware/jwtutil

Usage: jwtutil -secret=secret -encode -claims='{"user_id":111}'

Output: eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VyX2lkIjoxMTF9._cLJn0xFS0Mdr_4L_8XF8-8tv7bHyOQJXyWaNsSqlEs

MIT