auth - authentication via oauth2

This library provides "social login" with Github, Google, Facebook and Yandex as well as custom auth providers.

Multiple oauth2 providers can be used at the same time
Special dev provider allows local testing and development
JWT stored in a secure cookie with XSRF protection. Cookies can be session-only
Minimal scopes with user name, id and picture (avatar) only
Direct authentication with user's provided credential checker
Verified authentication with user's provided sender (email, im, etc)
Integrated avatar proxy with FS, boltdb and gridfs storage
Support of user-defined storage for avatars
Identicon for default avatars
Black list with user-defined validator
Multiple aud (audience) supported
Secure key with customizable SecretReader
Ability to store an extra information to token and retrieve on login
Pre-auth and post-auth hooks to handle custom use cases.
Middleware for easy integration into http routers
Wrappers to extract user info from the request

Install

go get -u github.com/go-pkgz/auth

Usage

Example with chi router:

func main() {
	/// define options
	options := auth.Opts{
		SecretReader: token.SecretFunc(func(id string) (string, error) { // secret key for JWT
			return "secret", nil
		}),
		TokenDuration:  time.Minute * 5, // token expires in 5 minutes
		CookieDuration: time.Hour * 24,  // cookie expires in 1 day and will enforce re-login
		Issuer:         "my-test-app",
		URL:            "http://127.0.0.1:8080",
		AvatarStore:    avatar.NewLocalFS("/tmp"),
		Validator: token.ValidatorFunc(func(_ string, claims token.Claims) bool {
			// allow only dev_* names
			return claims.User != nil && strings.HasPrefix(claims.User.Name, "dev_")
		}),
	}

	// create auth service with providers
	service := auth.NewService(options)
	service.AddProvider("github", "<Client ID>", "<Client Secret>")   // add github provider
	service.AddProvider("facebook", "<Client ID>", "<Client Secret>") // add facebook provider

	// retrieve auth middleware
	m := service.Middleware()

	// setup http server
	router := chi.NewRouter()
	router.Get("/open", openRouteHandler)                      // open api
	router.With(m.Auth).Get("/private", protectedRouteHandler) // protected api

	// setup auth routes
	authRoutes, avaRoutes := service.Handlers()
	router.Mount("/auth", authRoutes)  // add auth handlers
	router.Mount("/avatar", avaRoutes) // add avatar handler

	log.Fatal(http.ListenAndServe(":8080", router))
}

Middleware

github.com/go-pkgz/auth/middleware provides ready-to-use middleware.

middleware.Auth - requires authenticated user
middleware.Admin - requires authenticated and admin user
middleware.Trace - doesn't require authenticated user, but adds user info to request

Details

Generally, adding support of auth includes a few relatively simple steps:

Setup auth.Opts structure with all parameters. Each of them documented and most of parameters are optional and have sane defaults.
Create the new auth.Service with provided options.
Add all desirable authentication providers. Currently supported Github, Google, Facebook and Yandex
Retrieve middleware and http handlers from auth.Service
Wire auth and avatar handlers into http router as sub–routes.

API

For the example above authentication handlers wired as /auth and provides:

/auth/<provider>/login?id=<site_id>&from=<redirect_url> - site_id used as aud claim for the token and can be processed by SecretReader to load/retrieve/define different secrets. redirect_url is the url to redirect after successful login.
/avatar/<avatar_id> - returns the avatar (image). Links to those pictures added into user info automatically, for details see "Avatar proxy"
/auth/<provider>/logout and /auth/logout - invalidate "session" by removing JWT cookie
/auth/list - gives a json list of active providers
/auth/user - returns token.User (json)

User info

Middleware populates token.User to request's context. It can be loaded with token.GetUserInfo(r *http.Request) (user User, err error) or token.MustGetUserInfo(r *http.Request) User functions.

token.User object includes all fields retrieved from oauth2 provider:

Name - user name
ID - hash of user id
Picture - full link to proxied avatar (see "Avatar proxy")

It also has placeholders for fields application can populate with custom token.ClaimsUpdater (see "Customization")

IP - hash of user's IP address
Email - user's email
Attributes - map of string:any-value. To simplify management of this map some setters and getters provided, for example users.StrAttr, user.SetBoolAttr and so on. See user.go for more details.

Avatar proxy

Direct links to avatars won't survive any real-life usage if they linked from a public page. For example, page like this may have hundreds of avatars and, most likely, will trigger throttling on provider's side. To eliminate such restriction auth library provides an automatic proxy

On each login the proxy will retrieve user's picture and save it to AvatarStore
Local (proxied) link to avatar included in user's info (jwt token)
API for avatar removal provided as a part of AvatarStore
User can leverage one of the provided stores:
- avatar.LocalFS - file system, each avatar in a separate file
- avatar.BoltDB - single boltdb file (embedded KV store).
- avatar.GridFS - external GridFS (mongo db).
In case of need custom implementations of other stores can be passed in and used by auth library. Each store has to implement avatar.Store interface.
All avatar-related setup done as a part of auth.Opts and needs:
- AvatarStore - avatar store to use, i.e. avatar.NewLocalFS("/tmp/avatars")
- AvatarRoutePath - route prefix for direct links to proxied avatar. For example /api/v1/avatars will make full links like this - http://example.com/api/v1/avatars/1234567890123.image. The url will be stored in user's token and retrieved by middleware (see "User Info")
- AvatarResizeLimit - size (in pixels) used to resize the avatar. Pls note - resize happens once as a part of Put call, i.e. on login. 0 size (default) disables resizing.

Direct authentication

In addition to oauth2 providers auth.Service allows to use direct user-defined authentication. This is done by adding direct provider with auth.AddDirectProvider.

	service.AddDirectProvider("local", provider.CredCheckerFunc(func(user, password string) (ok bool, err error) {
		ok, err := checkUserSomehow(user, password) 
		return ok, err
	}))

Such provider acts like any other, i.e. will be registered as /auth/local/login.

The API for this provider - GET /auth/<name>/login?user=<user>&passwd=<password>&aud=<site_id>&session=[1|0]

note: password parameter doesn't have to be naked/real password and can be any kind of password hash prepared by caller.

Verified authentication

Another non-oauth2 provider allowing user-confirmed authentication, for example by email or slack or telegram. This is done by adding confirmed provider with auth.AddVerifProvider.

    msgTemplate := "Confirmation email, token: {{.Token}}"
	service.AddVerifProvider("email", msgTemplate, sender)

Message template may use the follow elements:

{{.Address}} - user address, for example email
{{.User}} - user name
{{.Token}} - confirmation token
{{.Site}} - site ID

Sender should be provided by end-user and implements a single function interface

type Sender interface {
	Send(address string, text string) error
}

For convenience a functional wrapper SenderFunc provided. Email sender provided in provider/sender package and can be used as Sender.

The API for this provider:

GET /auth/<name>/login?user=<user>&address=<adsress>&aud=<site_id>&from=<url> - send confirmation request to user
GET /auth/<name>/login?token=<conf.token>&sess=[1|0] - authorize with confirmation token

The provider acts like any other, i.e. will be registered as /auth/email/login.

Customization

There are several ways to adjust functionality of the library:

SecretReader - interface with a single method Get(aud string) string to return the secret used for JWT signing and verification
ClaimsUpdater - interface with Update(claims Claims) Claims method. This is the primary way to alter a token at login time and add any attributes, set ip, email, admin status and so on.
Validator - interface with Validate(token string, claims Claims) bool method. This is post-token hook and will be called on each request wrapped with Auth middleware. This will be the place for special logic to reject some tokens or users.

All of the interfaces above have corresponding Func adapters - SecretFunc, ClaimsUpdFunc and ValidatorFunc.

Implementing black list logic or some other filters

Restricting some users or some tokens is two step process:

ClaimsUpdater sets an attribute, like blocked (or allowed)
Validator checks the attribute and returns true/false

This technic used in the example code

The process can be simplified by doing all checks directly in Validator, but depends on particular case such solution can be too expensive because Validator runs on each request as a part of auth middleware. In contrast, ClaimsUpdater called on token creation/refresh only.

Multi-tenant services and support for different audiences

For complex systems a single authenticator may serve multiple distinct subsystems or multiple set of independent users. For example some SaaS offerings may need to provide different authentications for different customers and prevent use of tokens/cookies made by another customer.

Such functionality can be implemented in 3 different ways:

Different instances of auth.Service each one with different secret. Doing this way will ensure the highest level of isolation and cookies/tokens won't be even parsable across the instances. Practically such architecture can be too complicated and not always possible. – Handling "allowed audience" as a part of ClaimsUpdater and Validator chain. I.e. ClaimsUpdater sets a claim indicating expected audience code/id and Validator making sure it matches. This way a single auth.Service could handle multiple groups of auth tokens and reject some based on the audience.
Using the standard JWT aud claim. This method conceptually very similar to the previous one, but done by library internally and consumer don't need to define special ClaimsUpdater and Validator logic.

In order to allow aud support the list of allowed audiences should be passed in as opts.Audiences parameter. Non-empty value will trigger internal checks for token generation (will reject token creation fot alien aud) as well as Auth middleware.

Dev provider

Working with oauth2 providers can be a pain, especially during development phase. A special, development-only provider dev can make it less painful. This one can be registered directly, i.e. service.AddProvider("dev", "", "") and should be activated like this:

	// runs dev oauth2 server on :8084
	go func() {
		devAuthServer, err := service.DevAuth()
		if err != nil {
			log.Fatal(err)
		}
		devAuthServer.Run()
	}()

It will run fake aouth2 "server" on port :8084 and user could login with any user name. See example for more details.

Warning: this is not the real oauth2 server but just a small fake thing for development and testing only. Don't use dev provider with any production code.

Other ways to authenticate

In addition to the primary method (i.e. JWT cookie with XSRF header) there are two more ways to authenticate:

Send JWT header as X-JWT. This shouldn't be used for web application, however can be helpful for service-to-service authentication.
Send JWT token as query parameter, i.e. /something?token=<jwt>
Basic access authentication. This mode disabled by default and will be enabled if Opts.AdminPasswd defined. This will allow access with basic auth admin:<Opts.AdminPasswd> with user admin. Such method can be used for automation scripts.

Logging

By default this library doesn't print anything to stdout/stderr, however user can pass a logger implementing logger.L interface with a single method Logf(format string, args ...interface{}). Functional adapter for this interface included as logger.Func. There are two predefined implementations in the logger package - NoOp (prints nothing, default) and Std wrapping log.Printf from stdlib.

Register oauth2 providers

Authentication handled by external providers. You should setup oauth2 for all (or some) of them to allow users to authenticate. It is not mandatory to have all of them, but at least one should be correctly configured.

Google Auth Provider

Create a new project: https://console.developers.google.com/project
Choose the new project from the top right project dropdown (only if another project is selected)
In the project Dashboard center pane, choose "API Manager"
In the left Nav pane, choose "Credentials"
In the center pane, choose "OAuth consent screen" tab. Fill in "Product name shown to users" and hit save.
In the center pane, choose "Credentials" tab.
- Open the "New credentials" drop down
- Choose "OAuth client ID"
- Choose "Web application"
- Application name is freeform, choose something appropriate
- Authorized origins is your domain ex: https://example.mysite.com
- Authorized redirect URIs is the location of oauth2/callback constructed as domain + /auth/google/callback, ex: https://example.mysite.com/auth/google/callback
- Choose "Create"
Take note of the Client ID and Client Secret

instructions for google oauth2 setup borrowed from oauth2_proxy

GitHub Auth Provider

Create a new "OAuth App": https://github.com/settings/developers
Fill "Application Name" and "Homepage URL" for your site
Under "Authorization callback URL" enter the correct url constructed as domain + /auth/github/callback. ie https://example.mysite.com/auth/github/callback
Take note of the Client ID and Client Secret

Facebook Auth Provider

From https://developers.facebook.com select "My Apps" / "Add a new App"
Set "Display Name" and "Contact email"
Choose "Facebook Login" and then "Web"
Set "Site URL" to your domain, ex: https://example.mysite.com
Under "Facebook login" / "Settings" fill "Valid OAuth redirect URIs" with your callback url constructed as domain + /auth/facebook/callback
Select "App Review" and turn public flag on. This step may ask you to provide a link to your privacy policy.

Yandex Auth Provider

Create a new "OAuth App": https://oauth.yandex.com/client/new
Fill "App name" for your site
Under Platforms select "Web services" and enter "Callback URI #1" constructed as domain + /auth/yandex/callback. ie https://example.mysite.com/auth/yandex/callback
Select Permissions. You need following permissions only from the "Yandex.Passport API" section:
- Access to user avatar
- Access to username, first name and surname, gender
Fill out the rest of fields if needed
Take note of the ID and Password

For more details refer to Yandex OAuth and Yandex.Passport API documentation.

Status

The library extracted from remark42 project. The original code in production use on multiple sites and seems to work fine.

go-pkgz/auth library still in development and until version 1 released some breaking changes possible.

namreg/auth