#!/usr/bin/env python
# Startdate: 2021-06-17
# goals:
#   accept kerberos or ldap "authorization: basic gowinablz;nuiowekj==" auth, to create a cookie for a session that lasts for 15 minutes. use the cookie to get to protected URLs
# References:
#    https://code.tutsplus.com/tutorials/flask-authentication-with-ldap--cms-23101
#    https://www.techlifediary.com/python-web-development-tutorial-using-flask-session-cookies/
#    delete cookie https://stackoverflow.com/a/14386413/3569534
#    timeout sessions https://stackoverflow.com/a/11785722/3569534
#    future: https://code.tutsplus.com/tutorials/flask-authentication-with-ldap--cms-23101
#    better timeout session: https://stackoverflow.com/a/49891626/3569534
# Improve:
#    purge sessions after 15 minutes?
# Run:
#    FLASK_APP=session_app.py FLASK_DEBUG=1 flask run --host 0.0.0.0
# Dependencies:
#    apt-get install python3-flask
#    pip3 install Flask-kerberos kerberos

from flask import Flask, Response, redirect, url_for, render_template, request

from flask_kerberos import init_kerberos, requires_authentication, _unauthorized, _forbidden, _gssapi_authenticate
from flask import _request_ctx_stack as stack, make_response, session
#from flask.ext.login import LoginManager
import kerberos
from functools import wraps
from socket import gethostname
import binascii, datetime

from functools import wraps
import os

DEBUG=True
app = Flask(__name__)
app.config.from_object(__name__)
app.debug=True
secret_key_value = os.urandom(24)
secret_key_value_hex_encoded = binascii.hexlify(secret_key_value)
app.config['SECRET_KEY'] = secret_key_value_hex_encoded
#app.config['PERMANENT_SESSION_LIFETIME'] = datetime.timedelta(days=7)
#session.permanent = True
minutes = 2
app.permanent_session_lifetime=datetime.timedelta(minutes=minutes)

def requires_session(function):
   '''
   Requires a valid session, provided by cookie!
   '''
   @wraps(function)
   def decorated(*args, **kwargs):
      if not session:
         return Response("requires session",401)
      else:
         if 'user' not in session:
            return Response("User is not in this session.",401)
         s_user = session['user']
         c_user = request.cookies.get('user')
         print(f"session user: {s_user}")
         print(f"cookie user: {c_user}")
         if session['user'] != c_user:
            return Response("Wrong user for this session!.",401)
         # otherwise, everything is good!
         #return Response(f"session user: {s_user}<br/>cookie user: {c_user}", 200)
         # return to the passed function, from https://github.com/ArtemAngelchev/flask-basicauth-ldap/blob/master/flask_basicauth_ldap.py
         return function(*args,**kwargs)
      # catch-all
      return Response("requires session",401)
   return decorated

# imported from flask_kerberos and modified, because I want custom 401 message
def requires_authn_kerberos(function):
   '''
   Require that the wrapped view function only be called by users
   authenticated with Kerberos. The view function will have the authenticated
   users principal passed to it as its first argument.

   :param function: flask view function
   :type function: function
   :returns: decorated function
   :rtype: function
   '''
   @wraps(function)
   def decorated(*args, **kwargs):
      header = request.headers.get("Authorization")
      if header:
         ctx = stack.top
         token = ''.join(header.split()[1:])
         rc = _gssapi_authenticate(token)
         if rc == kerberos.AUTH_GSS_COMPLETE:
            response = function(ctx.kerberos_user, *args, **kwargs)
            response = make_response(response)
            if ctx.kerberos_token is not None:
               response.headers['WWW-Authenticate'] = ' '.join(['negotiate', ctx.kerberos_token])
            return response
         elif rc != kerberos.AUTH_GSS_CONTINUE:
            return _forbidden()
      return _unauthorized_kerberos()
   return decorated

def _unauthorized_kerberos():
   '''
   Indicate that authentication is required
   '''
   # from https://billstclair.com/html-redirect2.html
   return Response(f'<meta http-equiv="Refresh" content="4; url={url_for("login_ldap")}">Unauthorized! No kerberos auth provided. Trying <a href="{url_for("login_ldap")}">ldap</a> automatically in a moment.', 401, {'WWW-Authenticate': 'Negotiate'})

@app.route("/")
def index():
   return render_template('index.html')

@app.route("/open/")
def open():
   header = request.headers.get("Authorization")
   if header:
      print("Header!")
      token = ''.join(header.split()[1:])
      print("token",token)
   print("something")
   return "<html><body>here</body></html>", 200

@app.route("/protected/")
@requires_session
def protected_page():
   return protected_page_real()

def protected_page_real():
   s_user = session['user']
   c_user = request.cookies.get('user')
   cookie=request.cookies
   print(cookie)
   return render_template('view.html', c_user = c_user, s_user=s_user, cookie=cookie)

@app.route("/login/new")
def login_new():
   return redirect(url_for("login", new=""))

@app.route("/login/", methods=['POST','GET'])
#@requires_authn_kerberos
def login(user="None"):
   if request.method == "GET":
      if 'user' in session and request.cookies.get('user') == session['user'] and (not 'new' in request.args):
         return redirect(url_for("protected_page"))
      auth_header = request.headers.get("Authorization")
      if auth_header:
         if "negotiate" in auth_header:
            # assume we are already trying to log in with kerberos
            return redirect(url_for("login_kerberos"))
      # default, show login form
      return redirect(url_for("login_form"))
   elif request.method == "POST":
      # so far only the login form sends a POST to this endpoint.
      username=request.form['username']
      pw=request.form['password']
      #pw="******"
      args=""
      for i in request.args:
         args += str(i)
      #resp = Response(f"Login functionality still in progress. <br/>Args: {args}<br/>data: {request.data}</br>query_string: {request.query_string}<br/>values: {request.values}",200)
      ldap_result = ldap_login(username,pw)
      resp = Response(f"Login functionality still in progress. <br/>username: {username}<br/>password: {pw}<br/>form: {request.form}<br/>ldap result:{ldap_result}",200)
      return resp

def ldap_login(username,password):
   response = f"Trying user {username} with pw '{password}'"
   print(response)
   return response
   

@app.route("/login/kerberos")
@requires_authn_kerberos
def login_kerberos(user):
   resp = Response(f'<meta http-equiv="Refresh" content="1; url={url_for("protected_page")}">success with kerberos')
   #resp.headers['login'] = "from-kerberos"
   resp.set_cookie('user',user)
   resp.set_cookie('type',"kerberos")
   end_time = datetime.datetime.now(datetime.timezone.utc) + app.permanent_session_lifetime
   end_time_str = datetime.datetime.strftime(end_time,"%FT%TZ")
   resp.set_cookie('timestamp',end_time_str)
   session.permanent = True
   session['user']=user
   session['end_time'] = end_time_str
   return resp

# WORKHERE: ldap auth
# WIP 2021-06-18 17:42; make this unauthenticated GET send to a form.
@app.route("/login/ldap", methods=['POST','GET'])
#@app.route("/login/ldap/<user>")
def login_ldap(user = "none"):
   resp = Response(f"success, from user {user}")
   resp.headers['login'] = "from-ldap"
   resp.set_cookie('user',user)
   resp.set_cookie('type',"ldap")
   session['user']=user
   resp.set_cookie('timestamp',app.permanent_session_lifetime)
   return resp

@app.route("/login/form/", methods=['GET'])
def login_form():
   options = {
         "ldap": "ldap",
      }
   return render_template("login_form.html",login_url=url_for("login"),options=options)

@app.route("/logout")
def logout():
   resp = Response(f"logged out")
   # Doing anything with session here leaves a cookie.
   #session['user']=""
   resp.set_cookie('user','',expires=0)
   resp.set_cookie('type','',expires=0)
   resp.set_cookie('session','',expires=0)
   resp.set_cookie('timestamp','',expires=0)
   return resp

## This bumps the session lifetime to two minutes farther out from each web request with this session.
#@app.before_request
#def make_session_permanent():
#   session.permanent = True
#   session['end_time'] = datetime.datetime.now()+app.permanent_session_lifetime

# keytab from `/usr/sbin/ipa-getkeytab -p HTTP/d2-03a.ipa.example.com -k session.keytab`
os.environ['KRB5_KTNAME'] = "./session.keytab"
os.environ['KRB5_TRACE'] = "./kerberos.log"
init_kerberos(app, hostname="d2-03a.ipa.internal.com", service="HTTP")
if __name__ == '__main__':
   init_kerberos(app, hostname="d2-03a.ipa.internal.com", service="HTTP")
   app.run(host='0.0.0.0',debug=True)