from django.contrib.auth import authenticate, login
from django.contrib.auth.backends import ModelBackend
from django.db.models import Q
# 繼承View 實現基于類的用戶登陸
from django.views.generic.base import View 
from .models import UserProfile
# 重寫 authenticate 登陸驗證方法
class CustomBackend(ModelBackend):
  def authenticate(self, username=None, password=None, **kwargs):
    try:
     # 驗證用戶名或郵箱， Q提供了一個對象間的或（與&）運算
    user=UserProfile.objects.get(Q(username=username) | Q(email=username))
      # 后臺密碼為暗文，傳入的密碼為明文， 所以需要使用check_password()方法驗證密碼
      if user.check_password(password):
        # 驗證成功返回user對象
        return user 
    # 登陸失敗返回None
    except Exception as e:
      return None

# 基于類實現用戶登陸
class LoginView(View):
  # 會根據 method 調用 post或者get方法
  def get(self, request):
    # 如果method為 GET 重新返回登陸頁面
    return render(request, "login.html", {})

  def post(self, request):
    # 驗證每個字段是否合法
    login_form = LoginForm(request.POST)
    # 對每個字段進行預處理，如果不合法，直接提示錯誤信息
    pre_check = login_form.is_valid()
    # 如果合法
    if pre_check:
      # 從POST中取出用戶名和密碼
      user_name = request.POST.get("username", "")
      if UserProfile.objects.filter(email=user_name):
        return render(request, "register.html", {"register_form": register_form, "msg": "用戶已經存在"})
      pass_word = request.POST.get("password", "")
      # 此處為上面重寫的authenticate方法
      user = authenticate(username=user_name, password=pass_word)
      if user is not None:   # 如果成功返回對象，失敗返回None
        login(request, user) # 調用login方法登陸賬號
        return render(request, "index.html")
      else:
        # 登陸失敗
        return render(request, "login.html", {"msg":u"用戶名或密碼錯誤"})
    else:
      # form驗證失敗，給出錯誤信息
      return render(request, "login.html", {"login_form":login_form})

from django import forms
# 繼承forms.Form
class LoginForm(forms.Form):
  # 如果為空則報錯
  username = forms.CharField(required=True)
  # 同時也可以設定長度限制min_length、max_length
  password = forms.CharField(required=True, min_length=5)

<div class="form-group marb20 {% if login_form.errors.username %}errorput{% endif %}">

<div class="error btns login-form-tips" id="jsLoginTips">{% for key,error in login_form.errors.items %}{{ error }}{% endfor %} {{ msg }}</div>