From 8fad53065943cb5f909ae783db1b95f06faa8915 Mon Sep 17 00:00:00 2001
From: Frederick Muriuki Muriithi
Date: Thu, 25 Jul 2024 14:53:47 -0500
Subject: OAuth2 package: Handle OAuth2 related issues

Adds utilities to handle talking to the authentication/authorisation
server.
---
 uploader/oauth2/__init__.py |   1 +
 uploader/oauth2/client.py   | 101 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 102 insertions(+)
 create mode 100644 uploader/oauth2/__init__.py
 create mode 100644 uploader/oauth2/client.py

diff --git a/uploader/oauth2/__init__.py b/uploader/oauth2/__init__.py
new file mode 100644
index 0000000..aaea638
--- /dev/null
+++ b/uploader/oauth2/__init__.py
@@ -0,0 +1 @@
+"""Package to handle OAuth2 authentication/authorisation issues."""
diff --git a/uploader/oauth2/client.py b/uploader/oauth2/client.py
new file mode 100644
index 0000000..6e101ae
--- /dev/null
+++ b/uploader/oauth2/client.py
@@ -0,0 +1,101 @@
+"""OAuth2 client utilities."""
+from urllib.parse import urljoin
+from datetime import datetime, timedelta
+
+import requests
+from flask import current_app as app
+
+from pymonad.either import Left, Right
+
+from authlib.jose import jwt
+from authlib.jose import KeySet, JsonWebKey
+from authlib.jose.errors import BadSignatureError
+from authlib.integrations.requests_client import OAuth2Session
+
+from uploader import session
+
+SCOPE = ("profile group role resource register-client user masquerade "
+         "introspect migrate-data")
+
+
+def authserver_uri():
+    """Return URI to authorisation server."""
+    return app.config["AUTH_SERVER_URL"]
+
+
+def oauth2_clientid():
+    """Return the client id."""
+    return app.config["OAUTH2_CLIENT_ID"]
+
+
+def oauth2_clientsecret():
+    """Return the client secret."""
+    return app.config["OAUTH2_CLIENT_SECRET"]
+
+
+def __make_token_validator__(keys: KeySet):
+    """Make a token validator function."""
+    def __validator__(token: str):
+        try:
+            jwt.decode(token, keys)
+            return Right(token)
+        except BadSignatureError:
+            return Left("INVALID-TOKEN")
+
+    return __validator__
+
+
+def __validate_token__(sess_info):
+    """Validate that the token is really from the auth server."""
+    info = __update_auth_server_jwks__(sess_info)
+    info["user"]["token"] = info["user"]["token"].then(__make_token_validator__(
+        KeySet(JsonWebKey(key) for key in info.get(
+            "auth_server_jwks", {}).get(
+                "jwks", {"keys": []})["keys"])))
+    return session.save_session_info(info)
+
+
+def __update_auth_server_jwks__(sess_info):
+    """Updates the JWKs every 2 hours or so."""
+    jwks = sess_info.get("auth_server_jwks")
+    if bool(jwks):
+        last_updated = jwks.get("last-updated")
+        now = datetime.now().timestamp()
+        if bool(last_updated) and (now - last_updated) < timedelta(hours=2).seconds:
+            return __validate_token__({**sess_info, "auth_server_jwks": jwks})
+
+    jwksuri = urljoin(authserver_uri(), "auth/public-jwks")
+    return __validate_token__({
+        **sess_info,
+        "auth_server_jwks": {
+            "jwks": KeySet([
+                JsonWebKey.import_key(key)
+                for key in requests.get(jwksuri).json()["jwks"]]).as_dict(),
+            "last-updated": datetime.now().timestamp()
+        }
+    })
+
+
+def oauth2_client():
+    """Build the OAuth2 client for use fetching data."""
+    def __update_token__(token, refresh_token=None, access_token=None):# pylint: disable=[unused-argument]
+        """Update the token when refreshed."""
+        app.logger.debug(f"IN `{__name__}`:\n\trefresh_token: {refresh_token}"
+                         f"\n\taccess_token: {access_token}\n\ttoken: {token}")
+        session.set_user_token(token)
+
+    def __client__(token) -> OAuth2Session:
+        client = OAuth2Session(
+            oauth2_clientid(),
+            oauth2_clientsecret(),
+            scope=SCOPE,
+            token_endpoint=urljoin(authserver_uri(), "/auth/token"),
+            token_endpoint_auth_method="client_secret_post",
+            token=token,
+            update_token=__update_token__)
+        return client
+
+    __update_auth_server_jwks__(session.session_info())
+    return session.user_token().either(
+        lambda _notok: __client__(None),
+        __client__)
-- 
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