[Django]-Django allauth facebook redirects to signup when retrieved email matches an existing user's email?

I have solved it after digging in deep into google and source code of django and django-allauth

Problem being solved: I just want the ability to interchangeably login using facebook and google with same email id and always redirect to LOGIN_REDIRECT_URL after successful login, but django-allauth doesn’t let me do that. Instead, it presents me with a signup page which I don’t want.

Solution:: Use @receiver(pre_social_login) to call a function link_to_local_user() which logs in 1st and then raises ImmediateHttpResponse which in turn redirects to LOGIN_REDIRECT_URL

#! myproject.adapter.py
from allauth.account.adapter import DefaultAccountAdapter
from allauth.socialaccount.adapter import DefaultSocialAccountAdapter
from allauth.exceptions import ImmediateHttpResponse
from allauth.socialaccount.signals import pre_social_login
from allauth.account.utils import perform_login
from allauth.utils import get_user_model
from django.http import HttpResponse
from django.dispatch import receiver
from django.shortcuts import redirect
from django.conf import settings
import json


class MyLoginAccountAdapter(DefaultAccountAdapter):
    '''
    Overrides allauth.account.adapter.DefaultAccountAdapter.ajax_response to avoid changing
    the HTTP status_code to 400
    '''

    def get_login_redirect_url(self, request):
        """ 
        """
        if request.user.is_authenticated():
            return settings.LOGIN_REDIRECT_URL.format(
                id=request.user.id)
        else:
            return "/"


class MySocialAccountAdapter(DefaultSocialAccountAdapter):
    '''
    Overrides allauth.socialaccount.adapter.DefaultSocialAccountAdapter.pre_social_login to 
    perform some actions right after successful login
    '''
    def pre_social_login(self, request, sociallogin):
        pass    # TODOFuture: To perform some actions right after successful login

@receiver(pre_social_login)
def link_to_local_user(sender, request, sociallogin, **kwargs):
    ''' Login and redirect
    This is done in order to tackle the situation where user's email retrieved
    from one provider is different from already existing email in the database
    (e.g facebook and google both use same email-id). Specifically, this is done to
    tackle following issues:
    * https://github.com/pennersr/django-allauth/issues/215

    '''
    email_address = sociallogin.account.extra_data['email']
    User = get_user_model()
    users = User.objects.filter(email=email_address)
    if users:
        # allauth.account.app_settings.EmailVerificationMethod
        perform_login(request, users[0], email_verification='optional')
        raise ImmediateHttpResponse(redirect(settings.LOGIN_REDIRECT_URL.format(id=request.user.id)))


#! settings.py
ACCOUNT_AUTHENTICATION_METHOD = "email" # Defaults to username_email
ACCOUNT_USERNAME_REQUIRED = False       # Defaults to True
ACCOUNT_EMAIL_REQUIRED = True           # Defaults to False
SOCIALACCOUNT_QUERY_EMAIL = ACCOUNT_EMAIL_REQUIRED
SOCIALACCOUNT_AUTO_SIGNUP = True
SOCIALACCOUNT_EMAIL_REQUIRED = False
ACCOUNT_ADAPTER = "myproject.adapter.MyLoginAccountAdapter"
SOCIALACCOUNT_ADAPTER = 'myproject.adapter.MySocialAccountAdapter'
LOGIN_URL = "/"
LOGIN_REDIRECT_URL = "/users/{id}/mytags"