Output:
DEBUG:root:Validating LDAPLoginForm against LDAP
DEBUG:flask_ldap3_login:Opening connection with bind user 'XXXX@XXXX.COM'
DEBUG:flask_ldap3_login:Successfully bound to LDAP as 'XXXX@XXXX.COM' for search_bind method
DEBUG:flask_ldap3_login:Performing an LDAP Search using filter '(&(objectclass=person)(sAMAccountName=YYYY))', base 'ou=Users,ou=XXXX,dc=XXXX,dc=COM', and scope 'SUBTREE'
DEBUG:flask_ldap3_login:Opening connection with bind user 'CN=YYYY,OU=Admin Users,OU=Users,OU=XXXX,DC=XXXX,DC=COM'
DEBUG:flask_ldap3_login:Directly binding a connection to a server with user:'CN=YYYY,OU=Admin Users,OU=Users,OU=XXXX,DC=XXXX,DC=COM'
DEBUG:flask_ldap3_login:Authentication was successful for user 'YYYY'

Output:
DEBUG:root:Validating LDAPLoginForm against LDAP
DEBUG:flask_ldap3_login:Opening connection with bind user 'XXXX@XXXX.COM'
DEBUG:flask_ldap3_login:Destroying connection at <0x7f181f9ee2b0>
ERROR:flask_ldap3_login:Uninitialized ASN.1 value ("__len__" attribute looked up)

from flask import Flask

app = Flask(__name__)
app.config.from_object('config')

from app.ldauth.views import auth_blueprint
app.register_blueprint(auth_blueprint)

from flask import Flask, Blueprint, url_for
from flask_ldap3_login import LDAP3LoginManager
from flask_login import LoginManager, login_user, UserMixin, current_user
from flask import render_template_string, render_template, redirect
from flask_ldap3_login.forms import LDAPLoginForm
from app import app

auth_blueprint = Blueprint('ldauth',__name__,template_folder='templates')

login_manager = LoginManager(app)              
ldap_manager = LDAP3LoginManager(app)          
users = {}

class User(UserMixin):
    def __init__(self, dn, username, data):
        self.dn = dn
        self.username = username
        self.data = data

    def __repr__(self):
        return self.dn

    def get_id(self):
        return self.dn

@login_manager.user_loader
def load_user(id):
    if id in users:
        return users[id]
    return None


@ldap_manager.save_user
def save_user(dn, username, data, memberships):
    user = User(dn, username, data)
    users[dn] = user
    return user

@auth_blueprint.route('/login', methods=['GET', 'POST'])
def login():
    template = """
    {{ get_flashed_messages() }}
    {{ form.errors }}
    <form method="POST">
        <label>Username{{ form.username() }}</label>
        <label>Password{{ form.password() }}</label>
        {{ form.submit() }}
        {{ form.hidden_tag() }}
    </form>
    """

    # Instantiate a LDAPLoginForm which has a validator to check if the user
    # exists in LDAP.

    form = LDAPLoginForm()

    if form.validate_on_submit():
        # Successfully logged in, We can now access the saved user object
        # via form.user.
        login_user(form.user)  # Tell flask-login to log them in.

        # TODO: Validate next to ensure it is safe!
        return redirect(next)  # Send them home

    return render_template_string(template,form=form)