Login System Tutorial Part 4 - Login Access Debugging (Current Progress)

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Structure:

templates

login.html

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<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Login Form</title>
  </head>
  <body>
    <form method="POST">
      <!-- The assigned name attribute is equivalent to r.PostFormValue in
      Golang (e.g. r.PostFormValue("username") = "admin") -->
      <input type="text" name="username" placeholder="Username" value="{{.Username}}"><br>
      <input type="password" name="password" placeholder="Password" value="{{.Password}}"><br>

      <!-- The OTP field will be displayed if the user has OTPRequired
        enabled in the database and after the user enters a valid username and
        password.-->
      {{if .OTPRequired}}
      <input type="text" name="otp" placeholder="OTP"><br>
      {{end}}

      <br><button type="submit">Login</button><br>
    </form>

    {{if .ErrExists}}
    <p>
      <b style="color:red">{{.Err}}</b>
    </p>
    {{end}}
  </body>
</html>

views

login.go

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// LoginHandler verifies login data and creating sessions for users.
func LoginHandler(w http.ResponseWriter, r *http.Request) {
    // Initialize the fields that we need in the custom struct.
    type Context struct {
        Err         string
        ErrExists   bool
        OTPRequired bool
        Username    string
        Password    string
    }
    // Call the Context struct.
    c := Context{}

    // If the request method is POST
    if r.Method == "POST" {
        // This is a login request from the user.
        username := r.PostFormValue("username")
        username = strings.TrimSpace(strings.ToLower(username))
        password := r.PostFormValue("password")
        otp := r.PostFormValue("otp")

        // Login2FA login using username, password and otp for users with OTPRequired = true.
        session := uadmin.Login2FA(r, username, password, otp)

        // Check whether the session returned is nil or the user is not active.
        if session == nil || !session.User.Active {
            /* Assign the login validation here that will be used for UI displaying. ErrExists and
            Err fields are coming from the Context struct. */
            c.ErrExists = true
            c.Err = "Invalid username/password or inactive user"

        } else {
            // If the user has OTPRequired enabled, it will print the username and OTP in the terminal.
            if session.PendingOTP {
                uadmin.Trail(uadmin.INFO, "User: %s OTP: %s", session.User.Username, session.User.GetOTP())
            }

            /* As long as the username and password is valid, it will create a session cookie in the
            browser. */
            cookie, _ := r.Cookie("session")
            if cookie == nil {
                cookie = &http.Cookie{}
            }
            cookie.Name = "session"
            cookie.Value = session.Key
            cookie.Path = "/"
            cookie.SameSite = http.SameSiteStrictMode
            http.SetCookie(w, cookie)

            // Check for OTP
            if session.PendingOTP {
                /* After the user enters a valid username and password in the first part of the form, these
                values will be used on the second part in the UI where the OTP input field will be
                displayed afterwards. */
                c.Username = username
                c.Password = password
                c.OTPRequired = true

            } else {
                uadmin.Trail(uadmin.DEBUG, "Your login credentials are valid.")
            }
        }
    }

    // Render the login filepath and pass the context data object to the HTML file.
    uadmin.RenderHTML(w, r, "templates/login.html", c)
}

views_main.go

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package views

import (
    "net/http"
    "strings"
)

// MainHandler is the main handler for the login system.
func MainHandler(w http.ResponseWriter, r *http.Request) {
    // r.URL.Path creates a new path called "/login_system/"
    r.URL.Path = strings.TrimPrefix(r.URL.Path, "/login_system")
    r.URL.Path = strings.TrimSuffix(r.URL.Path, "/")

    // LoginHandler verifies login data and creating sessions for users.
    LoginHandler(w, r)
}

main.go

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package main

import (
    "net/http"

    // Specify the username that you used inside github.com folder
    "github.com/username/project_name/views"

    "github.com/uadmin/uadmin"
)

func main() {
    // Assign RootURL value as "/admin/" and Site Name as "Login System"
    // NOTE: This code works only if database does not exist yet.
    uadmin.RootURL = "/admin/"
    uadmin.SiteName = "Login System"

    // Login System Main Handler
    http.HandleFunc("/login_system/", uadmin.Handler(views.MainHandler))

    // Run the server
    uadmin.StartServer()
}