Add /login endpoint to server.py

.flake8

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+[flake8]
+per-file-ignores =
+    ./server.py:B901,E722

server.py

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+#!/usr/bin/env python3
+
+import subprocess
+import json
+import os
+import bcrypt
+from flask import Flask, request
+
+app = Flask(__name__)
+
+
+@app.route('/login', methods=['POST'])
+def en_login():
+    try:
+        password = request.values['password']
+    except KeyError:
+        return "Missing password", 400
+    with open('config.json') as f:
+        config = json.load(f)
+
+    if not bcrypt.checkpw(password.encode(), config["password"].encode()):
+        return "Unauthorized", 401
+
+    if os.path.isfile(os.path.expanduser('~/.the-long-night-pid')):
+        return "Already logged in"
+
+    with open(os.path.expanduser('~/.the-long-night-pid'), 'w') as f:
+        x = subprocess.Popen(["python3", "background.py"],
+                             start_new_session=True)
+        f.write(str(x.pid))
+
+    message = ("The correct password has been entered in The-Long-Night. "
+               "The ssh key will be added " + str(config["days"]) + " days "
+               "later. To prevent that from happenning, login to your server "
+               "and run `cancel-adding-key.sh` in The Long Night installation"
+               "directory.")
+
+    if config["matrix"]["enabled"]:
+        from backends import matrix
+        try:
+            matrix.send(config["matrix"], message)
+        except:
+            pass
+
+    if config["telegram"]["enabled"]:
+        from backends import telegram
+        try:
+            telegram.send(config["telegram"], message)
+        except:
+            pass
+
+    return ("Logged In. The ssh key will be added " + str(config["days"]) +
+            " day(s) later.")