ldap4gin

Authenticator for gin framework using ldap server

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Installing

Usual way for go module

go get -u github.com/vodolaz095/ldap4gin

Code was tested against popular osixia/openldap:1.4.0 container, with records generated using ldapaccountmanager/lam web ui.

Example

Working example is published in example/ subdirectory of this repo. In order to get working ldap server you need to start it with docker compose up -d and then edit users and groups in LDAP Account Manager on http://127.0.0.1:8085/lam/templates/login.php

package main

import (
   "bytes"
   "crypto/tls"
   "fmt"
   "log"
   "net/http"
   "time"

   "github.com/gin-contrib/sessions"
   "github.com/gin-contrib/sessions/cookie"
   "github.com/gin-gonic/gin"
   "github.com/vodolaz095/ldap4gin"
)

func main() {
   r := gin.Default()
   r.LoadHTMLGlob("views/*")
   // configuring options used to connect to LDAP database
   authenticator, err := ldap4gin.New(&ldap4gin.Options{
      Debug: gin.IsDebugging(),

      ConnectionString: "ldap://127.0.0.1:389",
      ReadonlyDN:       "cn=readonly,dc=vodolaz095,dc=life",
      ReadonlyPasswd:   "readonly",
      TLS:              &tls.Config{}, // nearly sane default values
      StartTLS:         false,

      UserBaseTpl: "uid=%s,ou=people,dc=vodolaz095,dc=life",
      ExtraFields: []string{"l"}, // get location too

      ExtractGroups: true,
      GroupsOU:      "ou=groups,dc=vodolaz095,dc=life",

      TTL: 10 * time.Second,
   })
   if err != nil {
      log.Fatalf("%s : while initializing ldap4gin authenticator", err)
   }
   log.Println("LDAP server dialed!")
   defer authenticator.Close()
   // Application should use any of compatible sessions offered by
   // https://github.com/gin-contrib/sessions module
   // CAUTION: secure cookie session storage has limits on user profile size!!!
   store := cookie.NewStore([]byte("secret"))
   r.Use(sessions.Sessions("mysession", store))

   // dashboard
   r.GET("/", func(c *gin.Context) {
      session := sessions.Default(c)
      flashes := session.Flashes()
      defer session.Save()
      //  extracting user's profile from context
      user, err := authenticator.Extract(c)
      if err != nil {
         if err.Error() == "unauthorized" { // render login page
            c.HTML(http.StatusUnauthorized, "unauthorized.html", gin.H{
               "flashes": flashes,
            })
            return
         }
         if err.Error() == "malformed username" {
            session.AddFlash("Malformed username")
            c.HTML(http.StatusUnauthorized, "unauthorized.html", gin.H{
               "flashes": flashes,
            })
            return
         }
         panic(err) // something wrong, like LDAP server stopped
      }
      // We can extract extra attributes for user using `user.Entry`
      buff := bytes.NewBuffer(nil)
      fmt.Fprintf(buff, "DN: %s\n", user.Entry.DN)
      for _, attr := range user.Entry.Attributes {
         fmt.Fprintf(buff, "%s: %s\n", attr.Name, attr.Values)
      }
      c.HTML(http.StatusOK, "profile.html", gin.H{
         "user":    user,
         "flashes": flashes,
         "raw":     buff.String(),
      })
   })

   // route to authorize user by username and password
   r.POST("/login", func(c *gin.Context) {
      session := sessions.Default(c)
      defer session.Save()
      username := c.PostForm("username")
      password := c.PostForm("password")
      log.Printf("User %s tries to authorize from %s...", username, c.ClientIP())
      err := authenticator.Authorize(c, username, password)
      if err != nil {
         log.Printf("User %s failed to authorize from %s because of %s", username, c.ClientIP(), err.Error())
         session.AddFlash(fmt.Sprintf("Authorization error  %s", err))
         c.Redirect(http.StatusFound, "/")
         return
      } else {
         log.Printf("User %s authorized from %s!", username, c.ClientIP())
         session.AddFlash(fmt.Sprintf("Welcome, %s!", username))
      }
      user, err := authenticator.Extract(c)
      if err != nil {
         log.Printf("%s : while extracting user", err)
      } else {
         log.Printf("user %s is extracted", user.DN)
      }
      c.Redirect(http.StatusFound, "/")
   })

   // route to terminate session and perform logout
   r.GET("/logout", func(c *gin.Context) {
      authenticator.Logout(c)
      c.Redirect(http.StatusFound, "/")
   })

   err = r.Run("0.0.0.0:3000")
   if err != nil {
      log.Fatalf("%s : while starting application", err)
   }
}

How it works?

You can read very good article in Russian language describing authentication process via LDAP.

Shortly, these steps are performed in this module:

1. we build DN using username parameter provided and UserBaseTpl of options

    authenticator, err := ldap4gin.New(ldap4gin.Options{
        Debug:            gin.IsDebugging(),
        ConnectionString: "ldap://127.0.0.1:389",
        UserBaseTpl:      "uid=%s,ou=people,dc=vodolaz095,dc=life",
        TLS:              &tls.Config{}, // nearly sane default values
        StartTLS:         false,
        ExtraFields:      []string{"l"}, // get location too
    })

    // some code

    // in gin handler
    err = authenticator.Authorize(c, username, password)

like this: uid=vodolaz095,ou=people,dc=vodolaz095,dc=life.

2. we try to perform bind using DN and password

    authenticator.LDAPConn.Bind(dn, password)

3. if we succeeded, it means user provided good password, and we can try to extract user profile calling this query:

searchRequest := ldap.NewSearchRequest(
    dn,                                // base DN
    ldap.ScopeBaseObject,              // scope
    ldap.NeverDerefAliases,            // DerefAliases
    0,                                 // size limit
    timeout,                           // timeout
    false,                             // types only
    fmt.Sprintf("(uid=%s)", username), // filter
    a.fields,                          // fields
    nil,                               // controls
)

4. After we extract data, we marshal it in User object, and store it in session using gob encoding. Its is worth notice that sometimes profile size is too big for session storage, and it can be wise not to store all users fields in session

5. If we enable extraction of groups by setting ExtractGroups:true, we will also perform bind by specual user with readonly access to all database in order to load groups of user we want to authenticate

Testing

1. docker compose up -d
2. Create test user account in LAM - http://127.0.0.1:8085/lam/templates/login.php, default password is someRandomPasswordToMakeHackersSad22223338888
3. Set test user's username and password as environment variables TEST_LDAP_USERNAME and TEST_LDAP_PASSWORD
4. Run tests by make check
5. Run example my make start and try to authorize as test user
6. Observe traces in Jaeger on http://127.0.0.1:16686/ for app ldap4gin_example

MIT License

Copyright (c) 2021 Anatolij Ostroumov

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.