weechat-matrix: Add support for single sign-on.

This patch adds support for the single sign-on login flow. If no
user/password is set Weechat will do a SSO login attempt.

contrib/matrix_sso_helper

@@ -0,0 +1,102 @@
+#!/usr/bin/env -S python3 -u
+# Copyright 2019 The Matrix.org Foundation CIC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+import asyncio
+import socket
+import json
+from random import choice
+from aiohttp import web
+
+# The browsers ban some known ports, the dynamic port range doesn't contain any
+# banned ports, so we use that.
+port_range = range(49152, 65535)
+
+shutdown_task = None
+
+
+def to_weechat(message):
+    print(json.dumps(message))
+
+
+async def get_token(request):
+    global shutdown_task
+
+    async def shutdown():
+        await asyncio.sleep(1)
+        raise KeyboardInterrupt
+
+    token = request.query.get("loginToken")
+
+    if not token:
+        raise KeyboardInterrupt
+
+    message = {
+        "type": "token",
+        "loginToken": token
+    }
+
+    # Send the token to weechat.
+    print(json.dumps(message))
+    # Initiate a shutdown.
+    shutdown_task = asyncio.ensure_future(shutdown())
+    # Respond to the browser.
+    return web.Response(text="Continuing in Weechat.")
+
+
+def bind_socket():
+    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+
+    while True:
+        port = choice(port_range)
+
+        try:
+            sock.bind(("localhost", port))
+        except OSError:
+            continue
+
+        return sock
+
+
+async def wait_for_shutdown_task(_):
+    if not shutdown_task:
+        return
+
+    try:
+        await shutdown_task
+    except KeyboardInterrupt:
+        pass
+
+
+def main():
+    app = web.Application()
+    app.add_routes([web.get('/', get_token)])
+    sock = bind_socket()
+    host, port = sock.getsockname()
+
+    message = {
+        "type": "redirectUrl",
+        "host": host,
+        "port": port
+    }
+
+    to_weechat(message)
+
+    app.on_shutdown.append(wait_for_shutdown_task)
+    web.run_app(app, sock=sock, handle_signals=True, print=None)
+
+
+if __name__ == "__main__":
+    main()