From cfda9d6cd15763e65fa851d964033e37f377239c Mon Sep 17 00:00:00 2001
From: Frederick Muriuki Muriithi
Date: Thu, 18 Apr 2024 20:15:25 +0300
Subject: Define and register grant for JWT tokens.

---
 .../oauth2/grants/jwt_bearer_grant.py              | 89 ++++++++++++++++++++++
 gn_auth/auth/authentication/oauth2/server.py       |  6 ++
 gn_auth/auth/authentication/users.py               |  4 +
 3 files changed, 99 insertions(+)
 create mode 100644 gn_auth/auth/authentication/oauth2/grants/jwt_bearer_grant.py

diff --git a/gn_auth/auth/authentication/oauth2/grants/jwt_bearer_grant.py b/gn_auth/auth/authentication/oauth2/grants/jwt_bearer_grant.py
new file mode 100644
index 0000000..492009c
--- /dev/null
+++ b/gn_auth/auth/authentication/oauth2/grants/jwt_bearer_grant.py
@@ -0,0 +1,89 @@
+"""JWT as Authorisation Grant"""
+import uuid
+from urllib.parse import urlparse
+from datetime import datetime, timedelta
+
+from flask import request, current_app as app
+
+from authlib.jose import jwt
+from authlib.jose.rfc7517.key_set import KeySet
+from authlib.oauth2.rfc7523.jwt_bearer import JWTBearerGrant as _JWTBearerGrant
+from authlib.oauth2.rfc7523.token import (
+    JWTBearerTokenGenerator as _JWTBearerTokenGenerator)
+
+from gn_auth.auth.authentication.users import user_by_id
+from gn_auth.auth.db.sqlite3 import connection, with_db_connection
+from gn_auth.auth.authentication.oauth2.models.oauth2client import client
+from gn_auth.auth.authentication.oauth2.grants.authorisation_code_grant import AuthorisationCodeGrant
+
+
+class JWTBearerTokenGenerator(_JWTBearerTokenGenerator):
+    """
+    A JSON Web Token formatted bearer token generator for jwt-bearer grant type.
+    """
+
+    DEFAULT_EXPIRES_IN = 300
+
+    def get_token_data(self, grant_type, client, expires_in=300, user=None, scope=None):
+        """Post process data to prevent JSON serialization problems."""
+        tokendata = super().get_token_data(
+            grant_type, client, expires_in, user, scope)
+        return {
+            **{
+                key: str(value) if key.endswith("_id") else value
+                for key, value in tokendata.items()
+            },
+            "sub": str(tokendata["sub"])}
+
+
+class JWTBearerGrant(_JWTBearerGrant, AuthorisationCodeGrant):
+    """Implement JWT as Authorisation Grant."""
+
+
+    def create_authorization_response(self, redirect_uri: str, grant_user):
+        resp = super().create_authorization_response(redirect_uri, grant_user)
+        headers = dict(resp[2])
+        location = urlparse(headers["Location"])
+        query = {
+            key.strip(): value.strip() for key, value in
+            (item.split("=") for  item in
+             (param.strip() for param in location.query.split("&")))}
+        parsed_redirect = urlparse(redirect_uri)
+        issued = datetime.now()
+        jwtkey = app.config["JWT_PRIVATE_KEY"]
+        jwttoken = jwt.encode(
+            {"alg": "RS256", "typ": "jwt", "kid": jwtkey.kid},
+            {
+                "iss": str(self.client.client_id),
+                "sub": str(grant_user.user_id),
+                "aud": f"{parsed_redirect.scheme}://{parsed_redirect.netloc}",
+                "exp": (issued + timedelta(minutes=5)),
+                "nbf": int(issued.timestamp()),
+                "iat": int(issued.timestamp()),
+                "jti": str(uuid.uuid4()),
+                "code": query["code"]},
+            jwtkey).decode("utf8")
+        return (302, "", [("Location", f"{location.geturl()}&jwt={jwttoken}")])
+
+
+    def resolve_issuer_client(self, issuer):
+        """Fetch client via "iss" in assertion claims."""
+        return with_db_connection(
+            lambda conn: self.server.query_client(issuer))
+
+
+    def resolve_client_key(self, client, headers, payload):
+        """Resolve client key to decode assertion data."""
+        return app.config["JWT_PUBLIC_KEY"]
+
+
+    def authenticate_user(self, subject):
+        """Authenticate user with the given assertion claims."""
+        return with_db_connection(lambda conn: user_by_id(conn, subject))
+
+
+    def has_granted_permission(self, client, user):
+        """
+        Check if the client has permission to access the given user's resource.
+        """
+        return True # TODO: Check this!!!
diff --git a/gn_auth/auth/authentication/oauth2/server.py b/gn_auth/auth/authentication/oauth2/server.py
index 0bce3d3..09a3449 100644
--- a/gn_auth/auth/authentication/oauth2/server.py
+++ b/gn_auth/auth/authentication/oauth2/server.py
@@ -14,6 +14,7 @@ from .models.oauth2token import OAuth2Token, save_token
 
 from .grants.password_grant import PasswordGrant
 from .grants.authorisation_code_grant import AuthorisationCodeGrant
+from .grants.jwt_bearer_grant import JWTBearerGrant, JWTBearerTokenGenerator
 
 from .endpoints.revocation import RevocationEndpoint
 from .endpoints.introspection import IntrospectionEndpoint
@@ -59,6 +60,11 @@ def setup_oauth2_server(app: Flask) -> None:
     # below
     server.register_grant(AuthorisationCodeGrant)
 
+    server.register_grant(JWTBearerGrant)
+    server.register_token_generator(
+        "urn:ietf:params:oauth:grant-type:jwt-bearer",
+        JWTBearerTokenGenerator(app.config["JWT_PRIVATE_KEY"]))
+
     # register endpoints
     server.register_endpoint(RevocationEndpoint)
     server.register_endpoint(IntrospectionEndpoint)
diff --git a/gn_auth/auth/authentication/users.py b/gn_auth/auth/authentication/users.py
index cb6a68e..1f364b8 100644
--- a/gn_auth/auth/authentication/users.py
+++ b/gn_auth/auth/authentication/users.py
@@ -17,6 +17,10 @@ class User:
     email: str
     name: str
 
+    def get_user_id(self):
+        """Get the user's ID."""
+        return self.user_id
+
 
 DUMMY_USER = User(user_id=UUID("a391cf60-e8b7-4294-bd22-ddbbda4b3530"),
                   email="gn3@dummy.user",
-- 
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