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auth.go
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auth.go
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package easyauth
import (
"context"
"crypto/rand"
"encoding/base64"
"fmt"
"html/template"
"log"
"net/http"
"strings"
"time"
"github.com/gorilla/mux"
)
//Role is a number representing a permission level.
//Specific roles will be defined by the host application.
//It is intended to be a bitmask.
//Each user will have a certain permission level associated, as can any endpoint or content.
//If the user permissions and the content requirement have any common bits (user & content != 0), then access will be granted.
type Role uint32
type User struct {
Username string
Access Role
Method string
Data interface{}
}
//AuthProvider is any source of user authentication. These core methods must be implemented by all providers.
type AuthProvider interface {
//Retreive a user from the current http request if present.
GetUser(r *http.Request) (*User, error)
}
//FormProvider is a provider that accepts login info from an html form.
type FormProvider interface {
AuthProvider
GetRequiredFields() []string
HandlePost(http.ResponseWriter, *http.Request)
}
//HTTPProvider is a provider that provides an http handler form managing its own login endpoints, for example oauth.
//Will receive all calls to /{providerName}/*
type HTTPProvider interface {
AuthProvider
http.Handler
}
type Logoutable interface {
//Logout allows the provider to delete any relevant cookies or session data in order to log the user out.
//The provider should not otherwise write to the response, or redirect
Logout(w http.ResponseWriter, r *http.Request)
}
type AuthManager interface {
AddProvider(string, AuthProvider)
LoginHandler() http.Handler
Wrapper(required Role) func(http.Handler) http.Handler
Wrap(next http.Handler, required Role) http.Handler
WrapFunc(next http.HandlerFunc, required Role) http.Handler
}
type namedProvider struct {
Name string
Provider AuthProvider
}
type namedFormProvider struct {
Name string
Provider FormProvider
}
type namedHTTPProvider struct {
Name string
Provider HTTPProvider
}
type authManager struct {
Providers []namedProvider
FormProviders []namedFormProvider
HTTPProviders []namedHTTPProvider
names map[string]bool
cookie *CookieManager
loginTemplate *template.Template
}
func New(opts ...Option) (AuthManager, error) {
var mgr = &authManager{
names: map[string]bool{},
cookie: &CookieManager{
duration: int((time.Hour * 24 * 30) / time.Second),
},
}
for _, opt := range opts {
if err := opt(mgr); err != nil {
return nil, err
}
}
if mgr.loginTemplate == nil {
mgr.loginTemplate = template.Must(template.New("login").Parse(loginTemplate))
}
return mgr, nil
}
func (m *authManager) AddProvider(name string, p AuthProvider) {
if _, ok := m.names[name]; ok {
panic(fmt.Errorf("Auth provider %s registered multiple times", name))
}
m.names[name] = true
m.Providers = append(m.Providers, namedProvider{name, p})
if form, ok := p.(FormProvider); ok {
m.FormProviders = append(m.FormProviders, namedFormProvider{name, form})
}
if httpp, ok := p.(HTTPProvider); ok {
m.HTTPProviders = append(m.HTTPProviders, namedHTTPProvider{name, httpp})
}
}
func (m *authManager) LoginHandler() http.Handler {
mx := mux.NewRouter()
mx.Path("/").Methods("GET").HandlerFunc(m.loginPage)
mx.Path("/out").Methods("GET").HandlerFunc(m.logout)
mx.Path("/deny").Methods("GET").HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
w.Write([]byte("<html><body><h1>Access denied</h1>You do not have access to the requested content."))
})
for _, form := range m.FormProviders {
mx.Path(fmt.Sprintf("/%s", form.Name)).Methods("POST").HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
m.postForm(w, r, form.Provider)
})
}
for _, httpp := range m.HTTPProviders {
mx.PathPrefix(fmt.Sprintf("/%s/", httpp.Name)).HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
m.delegateHTTP(w, r, httpp.Provider)
})
}
return mx
}
func (m *authManager) buildContext(w http.ResponseWriter, r *http.Request) *http.Request {
ctx := context.WithValue(r.Context(), cookieContextKey, m.cookie)
ctx = context.WithValue(ctx, redirectContextKey, func() {
m.redirect(w, r)
})
return r.WithContext(ctx)
}
//Wrapper returns a middleware constructor for the given auth level. This function can be used with middleware chains
//or by itself to create new handlers in the future
func (m *authManager) Wrapper(required Role) func(http.Handler) http.Handler {
return func(h http.Handler) http.Handler {
return m.Wrap(h, required)
}
}
func (m *authManager) Wrap(next http.Handler, required Role) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
orig := r
r = m.buildContext(w, r)
var u *User
var err error
for _, p := range m.Providers {
u, err = p.Provider.GetUser(r)
if err != nil {
log.Println(err)
continue
}
if u != nil {
r = orig //don't send intenral context to real handler
r = r.WithContext(context.WithValue(r.Context(), userContextKey, u))
break
}
}
if required == 0 {
//no permission needed
next.ServeHTTP(w, r)
} else if u == nil {
//logged out. redir to login
if strings.Contains(r.Header.Get("Accept"), "html") {
m.cookie.SetCookiePlain(w, redirCookirName, 10*60, r.URL.String())
http.Redirect(w, r, "/login/", http.StatusFound) //todo: configure this
} else {
http.Error(w, "Access Denied", http.StatusForbidden)
}
} else if u.Access&required == 0 {
//denied for permissions
if strings.Contains(r.Header.Get("Accept"), "html") {
m.cookie.SetCookiePlain(w, redirCookirName, 10*60, r.URL.String())
http.Redirect(w, r, "/login/deny", http.StatusFound)
} else {
http.Error(w, "Access Denied", http.StatusForbidden)
}
} else {
//has permission
next.ServeHTTP(w, r)
}
})
}
func (m *authManager) WrapFunc(next http.HandlerFunc, required Role) http.Handler {
return m.Wrap(next, required)
}
const (
errMsgCookieName = "errMsg"
redirCookirName = "redirTo"
)
func (m *authManager) loginPage(w http.ResponseWriter, r *http.Request) {
msg, err := m.cookie.ReadCookiePlain(r, errMsgCookieName)
if err == nil {
m.cookie.ClearCookie(w, errMsgCookieName)
}
var ctx = map[string]interface{}{
"Auth": m,
"Message": msg,
}
if err := m.loginTemplate.Execute(w, ctx); err != nil {
log.Printf("Error executing login template: %s", err)
}
}
func (m *authManager) logout(w http.ResponseWriter, r *http.Request) {
r = m.buildContext(w, r)
for _, p := range m.Providers {
if lo, ok := p.Provider.(Logoutable); ok {
lo.Logout(w, r)
}
}
http.Redirect(w, r, "/", 302)
}
type contextKeyType int
const (
cookieContextKey contextKeyType = iota
redirectContextKey
userContextKey
)
func (m *authManager) delegateHTTP(w http.ResponseWriter, r *http.Request, h HTTPProvider) {
r = m.buildContext(w, r)
h.ServeHTTP(w, r)
}
func (m *authManager) redirect(w http.ResponseWriter, r *http.Request) {
path := "/"
stored, err := m.cookie.ReadCookiePlain(r, redirCookirName)
if err == nil {
path = stored
m.cookie.ClearCookie(w, redirCookirName)
}
http.Redirect(w, r, path, http.StatusFound)
}
func (m *authManager) postForm(w http.ResponseWriter, r *http.Request, p FormProvider) {
defer func() {
if rc := recover(); rc != nil {
//set short-lived cookie with message and redirect to login page
m.cookie.SetCookiePlain(w, errMsgCookieName, 60, fmt.Sprint(rc))
http.Redirect(w, r, r.Header.Get("Referer"), http.StatusFound)
}
}()
r = m.buildContext(w, r)
p.HandlePost(w, r)
}
func GetCookieManager(r *http.Request) *CookieManager {
return r.Context().Value(cookieContextKey).(*CookieManager)
}
func GetRedirector(r *http.Request) func() {
return r.Context().Value(redirectContextKey).(func())
}
func GetUser(r *http.Request) *User {
u := r.Context().Value(userContextKey)
if u == nil {
return nil
}
return u.(*User)
}
//RandomString returns a random string of bytes length long, base64 encoded.
func RandomString(length int) string {
var dat = make([]byte, length)
rand.Read(dat)
return base64.StdEncoding.EncodeToString(dat)
}