15 files changed, 555 insertions, 57 deletions
diff --git a/gn3/auth/authentication/oauth2/__init__.py b/gn3/auth/authentication/oauth2/__init__.py
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/gn3/auth/authentication/oauth2/__init__.py
diff --git a/gn3/auth/authentication/oauth2/endpoints/__init__.py b/gn3/auth/authentication/oauth2/endpoints/__init__.py
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/gn3/auth/authentication/oauth2/endpoints/__init__.py
diff --git a/gn3/auth/authentication/oauth2/endpoints/introspection.py b/gn3/auth/authentication/oauth2/endpoints/introspection.py
new file mode 100644
index 0000000..a567363
--- /dev/null
+++ b/gn3/auth/authentication/oauth2/endpoints/introspection.py
@@ -0,0 +1,48 @@
+"""Handle introspection of tokens."""
+import datetime
+from urllib.parse import urlparse
+
+from flask import request as flask_request
+from authlib.oauth2.rfc7662 import (
+    IntrospectionEndpoint as _IntrospectionEndpoint)
+
+from gn3.auth.authentication.oauth2.models.oauth2token import OAuth2Token
+
+from .utilities import query_token as _query_token
+
+def get_token_user_sub(token: OAuth2Token) -> str:# pylint: disable=[unused-argument]
+    """
+    Return the token's subject as defined in
+    https://datatracker.ietf.org/doc/html/rfc7519#section-4.1.2
+    """
+    ## For now a dummy return to prevent issues.
+    return "sub"
+
+class IntrospectionEndpoint(_IntrospectionEndpoint):
+    """Introspect token."""
+    def query_token(self, token_string: str, token_type_hint: str):
+        """Query the token."""
+        return _query_token(self, token_string, token_type_hint)
+
+    def introspect_token(self, token: OAuth2Token) -> dict:# pylint: disable=[no-self-use]
+        """Return the introspection information."""
+        url = urlparse(flask_request.url)
+        return {
+            "active": True,
+            "scope": token.get_scope(),
+            "client_id": token.client.client_id,
+            "username": token.user.name,
+            "token_type": token.token_type,
+            "exp": int(token.expires_at.timestamp()),
+            "iat": int(token.issued_at.timestamp()),
+            "nbf": int(
+                (token.issued_at - datetime.timedelta(seconds=120)).timestamp()),
+            # "sub": get_token_user_sub(token),
+            "aud": token.client.client_id,
+            "iss": f"{url.scheme}://{url.netloc}",
+            "jti": token.token_id
+        }
+
+    def check_permission(self, token, client, request):# pylint: disable=[unused-argument, no-self-use]
+        """Check that the client has permission to introspect token."""
+        return client.client_type == "internal"
diff --git a/gn3/auth/authentication/oauth2/endpoints/revocation.py b/gn3/auth/authentication/oauth2/endpoints/revocation.py
new file mode 100644
index 0000000..0693c2d
--- /dev/null
+++ b/gn3/auth/authentication/oauth2/endpoints/revocation.py
@@ -0,0 +1,21 @@
+"""Handle token revocation."""
+
+from flask import current_app
+from authlib.oauth2.rfc7009 import RevocationEndpoint as _RevocationEndpoint
+
+from gn3.auth import db
+from gn3.auth.authentication.oauth2.models.oauth2token import (
+    save_token, OAuth2Token, revoke_token)
+
+from .utilities import query_token as _query_token
+
+class RevocationEndpoint(_RevocationEndpoint):
+    """Revoke the tokens"""
+    def query_token(self, token_string: str, token_type_hint: str):
+        """Query the token."""
+        return _query_token(self, token_string, token_type_hint)
+
+    def revoke_token(self, token: OAuth2Token, request):
+        """Revoke token `token`."""
+        with db.connection(current_app.config["AUTH_DB"]) as conn:
+            save_token(conn, revoke_token(token))
diff --git a/gn3/auth/authentication/oauth2/endpoints/utilities.py b/gn3/auth/authentication/oauth2/endpoints/utilities.py
new file mode 100644
index 0000000..299f151
--- /dev/null
+++ b/gn3/auth/authentication/oauth2/endpoints/utilities.py
@@ -0,0 +1,30 @@
+"""endpoint utilities"""
+from typing import Any, Optional
+
+from flask import current_app
+from pymonad.maybe import Nothing
+
+from gn3.auth import db
+from gn3.auth.authentication.oauth2.models.oauth2token import (
+    OAuth2Token, token_by_access_token, token_by_refresh_token)
+
+def query_token(# pylint: disable=[unused-argument]
+        endpoint_object: Any, token_str: str, token_type_hint) -> Optional[
+            OAuth2Token]:
+    """Retrieve the token from the database."""
+    __identity__ = lambda val: val
+    token = Nothing
+    with db.connection(current_app.config["AUTH_DB"]) as conn:
+        if token_type_hint == "access_token":
+            token = token_by_access_token(conn, token_str)
+        if token_type_hint == "access_token":
+            token = token_by_refresh_token(conn, token_str)
+
+        return token.maybe(
+            token_by_access_token(conn, token_str).maybe(
+                token_by_refresh_token(conn, token_str).maybe(
+                    None, __identity__),
+                __identity__),
+            __identity__)
+
+    return None
diff --git a/gn3/auth/authentication/oauth2/grants/__init__.py b/gn3/auth/authentication/oauth2/grants/__init__.py
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/gn3/auth/authentication/oauth2/grants/__init__.py
diff --git a/gn3/auth/authentication/oauth2/grants/authorisation_code_grant.py b/gn3/auth/authentication/oauth2/grants/authorisation_code_grant.py
new file mode 100644
index 0000000..d398192
--- /dev/null
+++ b/gn3/auth/authentication/oauth2/grants/authorisation_code_grant.py
@@ -0,0 +1,45 @@
+"""Classes and function for Authorisation Code flow."""
+import uuid
+from typing import Optional
+
+from flask import current_app as app
+from authlib.oauth2.rfc6749 import grants
+
+from gn3.auth import db
+from gn3.auth.authentication.users import User
+
+class AuthorisationCodeGrant(grants.AuthorizationCodeGrant):
+    """Implement the 'Authorisation Code' grant."""
+    TOKEN_ENDPOINT_AUTH_METHODS = ["client_secret_basic", "client_secret_post"]
+
+    def save_authorization_code(self, code, request):
+        """Persist the authorisation code to database."""
+        raise Exception("NOT IMPLEMENTED!", self, code, request)
+
+    def query_authorization_code(self, code, client):
+        """Retrieve the code from the database."""
+        raise Exception("NOT IMPLEMENTED!", self, code, client)
+
+    def delete_authorization_code(self, authorization_code):# pylint: disable=[no-self-use]
+        """Delete the authorisation code."""
+        with db.connection(app.config["AUTH_DB"]) as conn:
+            with db.cursor(conn) as cursor:
+                cursor.execute(
+                    "DELETE FROM authorisation_code WHERE code_id=?",
+                    (str(authorization_code.code_id),))
+
+    def authenticate_user(self, authorization_code) -> Optional[User]:
+        """Authenticate the user who own the authorisation code."""
+        query = (
+            "SELECT users.* FROM authorisation_code LEFT JOIN users "
+            "ON authorisation_code.user_id=users.user_id "
+            "WHERE authorisation_code.code=?")
+        with db.connection(app.config["AUTH_DB"]) as conn:
+            with db.cursor(conn) as cursor:
+                cursor.execute(query, (str(authorization_code.user_id),))
+                res = cursor.fetchone()
+                if res:
+                    return User(
+                        uuid.UUID(res["user_id"]), res["email"], res["name"])
+
+        return None
diff --git a/gn3/auth/authentication/oauth2/grants/password_grant.py b/gn3/auth/authentication/oauth2/grants/password_grant.py
new file mode 100644
index 0000000..91fdb7c
--- /dev/null
+++ b/gn3/auth/authentication/oauth2/grants/password_grant.py
@@ -0,0 +1,18 @@
+"""Allows users to authenticate directly."""
+
+from flask import current_app as app
+from authlib.oauth2.rfc6749 import grants
+
+from gn3.auth import db
+from gn3.auth.authentication.users import valid_login, user_by_email
+
+class PasswordGrant(grants.ResourceOwnerPasswordCredentialsGrant):
+    """Implement the 'Password' grant."""
+    TOKEN_ENDPOINT_AUTH_METHODS = ["client_secret_basic", "client_secret_post"]
+
+    def authenticate_user(self, username, password):
+        "Authenticate the user with their username and password."
+        with db.connection(app.config["AUTH_DB"]) as conn:
+            return user_by_email(conn, username).maybe(
+                None,
+                lambda user: valid_login(conn, user, password))
diff --git a/gn3/auth/authentication/oauth2/models/__init__.py b/gn3/auth/authentication/oauth2/models/__init__.py
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/gn3/auth/authentication/oauth2/models/__init__.py
diff --git a/gn3/auth/authentication/oauth2/models/oauth2client.py b/gn3/auth/authentication/oauth2/models/oauth2client.py
new file mode 100644
index 0000000..2ee7858
--- /dev/null
+++ b/gn3/auth/authentication/oauth2/models/oauth2client.py
@@ -0,0 +1,141 @@
+"""OAuth2 Client model."""
+import json
+import uuid
+import datetime
+from typing import NamedTuple, Sequence
+
+from pymonad.maybe import Just, Maybe, Nothing
+
+from gn3.auth import db
+from gn3.auth.authentication.users import User, user_by_id
+
+class OAuth2Client(NamedTuple):
+    """
+    Client to the OAuth2 Server.
+
+    This is defined according to the mixin at
+    https://docs.authlib.org/en/latest/specs/rfc6749.html#authlib.oauth2.rfc6749.ClientMixin
+    """
+    client_id: uuid.UUID
+    client_secret: str
+    client_id_issued_at: datetime.datetime
+    client_secret_expires_at: datetime.datetime
+    client_metadata: dict
+    user: User
+
+    def check_client_secret(self, client_secret: str) -> bool:
+        """Check whether the `client_secret` matches this client."""
+        return self.client_secret == client_secret
+
+    @property
+    def token_endpoint_auth_method(self) -> str:
+        """Return the token endpoint authorisation method."""
+        return self.client_metadata.get("token_endpoint_auth_method", ["none"])
+
+    @property
+    def client_type(self) -> str:
+        """Return the token endpoint authorisation method."""
+        return self.client_metadata.get("client_type", "public")
+
+    def check_endpoint_auth_method(self, method: str, endpoint: str) -> bool:
+        """
+        Check if the client supports the given method for the given endpoint.
+
+        Acceptable methods:
+        * none: Client is a public client and does not have a client secret
+        * client_secret_post: Client uses the HTTP POST parameters
+        * client_secret_basic: Client uses HTTP Basic
+        """
+        if endpoint == "token":
+            return (method in self.token_endpoint_auth_method
+                    and method == "client_secret_post")
+        if endpoint in ("introspection", "revoke"):
+            return (method in self.token_endpoint_auth_method
+                    and method == "client_secret_basic")
+        return False
+
+    @property
+    def id(self):# pylint: disable=[invalid-name]
+        """Return the client_id."""
+        return self.client_id
+
+    @property
+    def grant_types(self) -> Sequence[str]:
+        """
+        Return the grant types that this client supports.
+
+        Valid grant types:
+        * authorisation_code
+        * implicit
+        * client_credentials
+        * password
+        """
+        return self.client_metadata.get("grant_types", [])
+
+    def check_grant_type(self, grant_type: str) -> bool:
+        """
+        Validate that client can handle the given grant types
+        """
+        return grant_type in self.grant_types
+
+    @property
+    def redirect_uris(self) -> Sequence[str]:
+        """Return the redirect_uris that this client supports."""
+        return self.client_metadata.get('redirect_uris', [])
+
+    def check_redirect_uri(self, redirect_uri: str) -> bool:
+        """
+        Check whether the given `redirect_uri` is one of the expected ones.
+        """
+        return redirect_uri in self.redirect_uris
+
+    @property
+    def response_types(self) -> Sequence[str]:
+        """Return the response_types that this client supports."""
+        return self.client_metadata.get("response_types", [])
+
+    def check_response_type(self, response_type: str) -> bool:
+        """Check whether this client supports `response_type`."""
+        return response_type in self.response_types
+
+    @property
+    def scope(self) -> Sequence[str]:
+        """Return valid scopes for this client."""
+        return tuple(set(self.client_metadata.get("scope", [])))
+
+    def get_allowed_scope(self, scope: str) -> str:
+        """Return list of scopes in `scope` that are supported by this client."""
+        if not bool(scope):
+            return ""
+        requested = scope.split()
+        return " ".join(sorted(set(
+            scp for scp in requested if scp in self.scope)))
+
+    def get_client_id(self):
+        """Return this client's identifier."""
+        return self.client_id
+
+    def get_default_redirect_uri(self) -> str:
+        """Return the default redirect uri"""
+        return self.client_metadata.get("default_redirect_uri", "")
+
+def client(conn: db.DbConnection, client_id: uuid.UUID) -> Maybe:
+    """Retrieve a client by its ID"""
+    with db.cursor(conn) as cursor:
+        cursor.execute(
+            "SELECT * FROM oauth2_clients WHERE client_id=?", (str(client_id),))
+        result = cursor.fetchone()
+        if result:
+            return Just(
+                OAuth2Client(uuid.UUID(result["client_id"]),
+                             result["client_secret"],
+                             datetime.datetime.fromtimestamp(
+                                 result["client_id_issued_at"]),
+                             datetime.datetime.fromtimestamp(
+                                 result["client_secret_expires_at"]),
+                             json.loads(result["client_metadata"]),
+                             user_by_id( # type: ignore[misc]
+                                 conn, uuid.UUID(result["user_id"])).maybe(
+                                     None, lambda usr: usr)))
+
+    return Nothing
diff --git a/gn3/auth/authentication/oauth2/models/oauth2token.py b/gn3/auth/authentication/oauth2/models/oauth2token.py
new file mode 100644
index 0000000..70421b4
--- /dev/null
+++ b/gn3/auth/authentication/oauth2/models/oauth2token.py
@@ -0,0 +1,119 @@
+"""OAuth2 Token"""
+import uuid
+import datetime
+from typing import NamedTuple, Optional, Sequence
+
+from pymonad.maybe import Just, Maybe, Nothing
+
+from gn3.auth import db
+from gn3.auth.authentication.users import User, user_by_id
+
+from .oauth2client import client, OAuth2Client
+
+class OAuth2Token(NamedTuple):
+    """Implement Tokens for OAuth2."""
+    token_id: uuid.UUID
+    client: OAuth2Client
+    token_type: str
+    access_token: str
+    refresh_token: Optional[str]
+    scope: Sequence[str]
+    revoked: bool
+    issued_at: datetime.datetime
+    expires_in: int
+    user: User
+
+    @property
+    def expires_at(self) -> datetime.datetime:
+        """Return the time when the token expires."""
+        return self.issued_at + datetime.timedelta(seconds=self.expires_in)
+
+    def check_client(self, client: OAuth2Client) -> bool:# pylint: disable=[redefined-outer-name]
+        """Check whether the token is issued to given `client`."""
+        return client.client_id == self.client.client_id
+
+    def get_expires_in(self) -> int:
+        """Return the `expires_in` value for the token."""
+        return self.expires_in
+
+    def get_scope(self) -> str:
+        """Return the valid scope for the token."""
+        return " ".join(self.scope)
+
+    def is_expired(self) -> bool:
+        """Check whether the token is expired."""
+        return self.expires_at < datetime.datetime.now()
+
+    def is_revoked(self):
+        """Check whether the token has been revoked."""
+        return self.revoked
+
+def __token_from_resultset__(conn: db.DbConnection, rset) -> Maybe:
+    the_client = client(conn, uuid.UUID(rset["client_id"]))
+    the_user = user_by_id(conn, uuid.UUID(rset["user_id"]))
+    __identity__ = lambda val: val
+
+    if the_client.is_just() and the_user.is_just():
+        return Just(OAuth2Token(token_id=uuid.UUID(rset["token_id"]),
+                                client=the_client.maybe(None, __identity__),
+                                token_type=rset["token_type"],
+                                access_token=rset["access_token"],
+                                refresh_token=rset["refresh_token"],
+                                scope=rset["scope"].split(None),
+                                revoked=(rset["revoked"] == 1),
+                                issued_at=datetime.datetime.fromtimestamp(
+                                    rset["issued_at"]),
+                                expires_in=rset["expires_in"],
+                                user=the_user.maybe(None, __identity__)))
+
+    return Nothing
+
+def token_by_access_token(conn: db.DbConnection, token_str: str) -> Maybe:
+    """Retrieve token by its token string"""
+    with db.cursor(conn) as cursor:
+        cursor.execute("SELECT * FROM oauth2_tokens WHERE access_token=?",
+                       (token_str,))
+        res = cursor.fetchone()
+        if res:
+            return __token_from_resultset__(conn, res)
+
+    return Nothing
+
+def token_by_refresh_token(conn: db.DbConnection, token_str: str) -> Maybe:
+    """Retrieve token by its token string"""
+    with db.cursor(conn) as cursor:
+        cursor.execute(
+            "SELECT * FROM oauth2_tokens WHERE refresh_token=?",
+            (token_str,))
+        res = cursor.fetchone()
+        if res:
+            return __token_from_resultset__(conn, res)
+
+    return Nothing
+
+def revoke_token(token: OAuth2Token) -> OAuth2Token:
+    """
+    Return a new token derived from `token` with the `revoked` field set to
+    `True`.
+    """
+    return OAuth2Token(
+        token_id=token.token_id, client=token.client,
+        token_type=token.token_type, access_token=token.access_token,
+        refresh_token=token.refresh_token, scope=token.scope, revoked=True,
+        issued_at=token.issued_at, expires_in=token.expires_in, user=token.user)
+
+def save_token(conn: db.DbConnection, token: OAuth2Token) -> None:
+    """Save/Update the token."""
+    with db.cursor(conn) as cursor:
+        cursor.execute(
+            "INSERT INTO oauth2_tokens VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)",
+            (str(token.token_id), str(token.client.client_id), token.token_type,
+             token.access_token, token.refresh_token, token.scope,
+             1 if token.revoked else 0, int(token.issued_at.timestamp()),
+             token.expires_in, str(token.user.user_id)))
+        ## If already exists
+        # cursor.execute(
+        #     ("UPDATE oauth2_tokens SET refresh_token=?, revoked=?, "
+        #      "expires_in=? WHERE token_id=?"),
+        #     (token.refresh_token, token.scope, 1 if token.revoked else 0,
+        #      token.expires_in, str(token.token_id)))
diff --git a/gn3/auth/authentication/oauth2/server.py b/gn3/auth/authentication/oauth2/server.py
new file mode 100644
index 0000000..960625d
--- /dev/null
+++ b/gn3/auth/authentication/oauth2/server.py
@@ -0,0 +1,63 @@
+"""Initialise the OAuth2 Server"""
+import uuid
+import datetime
+from typing import Callable
+
+from flask import Flask, current_app
+from authlib.integrations.flask_oauth2 import AuthorizationServer
+# from authlib.integrations.sqla_oauth2 import (
+#     create_save_token_func, create_query_client_func)
+
+from gn3.auth import db
+
+from .models.oauth2client import client
+from .models.oauth2token import OAuth2Token, save_token
+
+from .grants.password_grant import PasswordGrant
+# from .grants.authorisation_code_grant import AuthorisationCodeGrant
+
+from .endpoints.revocation import RevocationEndpoint
+from .endpoints.introspection import IntrospectionEndpoint
+
+def create_query_client_func() -> Callable:
+    """Create the function that loads the client."""
+    def __query_client__(client_id: uuid.UUID):
+        # use current_app rather than passing the db_uri to avoid issues
+        # when config changes, e.g. while testing.
+        with db.connection(current_app.config["AUTH_DB"]) as conn:
+            return client(conn, client_id).maybe(None, lambda clt: clt) # type: ignore[misc]
+
+    return __query_client__
+
+def create_save_token_func(token_model: type) -> Callable:
+    """Create the function that saves the token."""
+    def __save_token__(token, request):
+        with db.connection(current_app.config["AUTH_DB"]) as conn:
+            save_token(
+                conn, token_model(
+                    token_id=uuid.uuid4(), client=request.client,
+                    user=request.client.user,
+                    **{
+                        "refresh_token": None, "revoked": False,
+                        "issued_at": datetime.datetime.now(),
+                        **token
+                    }))
+
+    return __save_token__
+
+def setup_oauth2_server(app: Flask) -> None:
+    """Set's up the oauth2 server for the flask application."""
+    server = AuthorizationServer()
+    server.register_grant(PasswordGrant)
+    # server.register_grant(AuthorisationCodeGrant)
+
+    # register endpoints
+    server.register_endpoint(RevocationEndpoint)
+    server.register_endpoint(IntrospectionEndpoint)
+
+    # init server
+    server.init_app(
+        app,
+        query_client=create_query_client_func(),
+        save_token=create_save_token_func(OAuth2Token))
+    app.config["OAUTH2_SERVER"] = server
diff --git a/gn3/auth/authentication/oauth2/views.py b/gn3/auth/authentication/oauth2/views.py
new file mode 100644
index 0000000..58fa6d4
--- /dev/null
+++ b/gn3/auth/authentication/oauth2/views.py
@@ -0,0 +1,42 @@
+"""Endpoints for the oauth2 server"""
+import uuid
+
+from flask import Blueprint, current_app as app
+
+from .endpoints.revocation import RevocationEndpoint
+from .endpoints.introspection import IntrospectionEndpoint
+
+oauth2 = Blueprint("oauth2", __name__)
+
+@oauth2.route("/register-client", methods=["GET", "POST"])
+def register_client():
+    """Register an OAuth2 client."""
+    return "WOULD REGISTER ..."
+
+@oauth2.route("/delete-client/<uuid:client_id>", methods=["GET", "POST"])
+def delete_client(client_id: uuid.UUID):
+    """Delete an OAuth2 client."""
+    return f"WOULD DELETE OAUTH2 CLIENT {client_id}."
+
+@oauth2.route("/authorise", methods=["GET", "POST"])
+def authorise():
+    """Authorise a user"""
+    return "WOULD AUTHORISE THE USER."
+
+@oauth2.route("/token", methods=["POST"])
+def token():
+    """Retrieve the authorisation token."""
+    server = app.config["OAUTH2_SERVER"]
+    return server.create_token_response()
+
+@oauth2.route("/revoke", methods=["POST"])
+def revoke_token():
+    """Revoke the token."""
+    return app.config["OAUTH2_SERVER"].create_endpoint_response(
+        RevocationEndpoint.ENDPOINT_NAME)
+
+@oauth2.route("/introspect", methods=["POST"])
+def introspect_token():
+    """Provide introspection information for the token."""
+    return app.config["OAUTH2_SERVER"].create_endpoint_response(
+        IntrospectionEndpoint.ENDPOINT_NAME)
diff --git a/gn3/auth/authentication/routes.py b/gn3/auth/authentication/routes.py
deleted file mode 100644
index 3b288d7..0000000
--- a/gn3/auth/authentication/routes.py
+++ /dev/null
@@ -1,57 +0,0 @@
-import requests
-
-import bcrypt
-from flask import flash, jsonify, request, session, Blueprint
-
-from gn3.auth import db
-from gn3.settings import AUTH_DB
-
-from .users import User, user_by_email
-
-auth_routes = Blueprint("auth", __name__)
-
-def valid_login(conn: db.DbConnection, user: User, password: str) -> bool:
-    """Check the validity of the provided credentials for login."""
-    with db.cursor(conn) as cursor:
-        cursor.execute(
-            ("SELECT * FROM users LEFT JOIN user_credentials "
-             "ON users.user_id=user_credentials.user_id "
-             "WHERE users.user_id=?"),
-            (str(user.user_id),))
-        row = cursor.fetchone()
-
-    if row == None:
-        return False
-
-    return bcrypt.checkpw(password.encode("utf-8"), row["password"])
-
-@auth_routes.route("/login", methods=["POST"])
-def login():
-    """Log in the user."""
-    print(request.cookies)
-    if session.get("user"):
-        flash("Already logged in!", "alert-warning")
-        print(f"ALREADY LOGGED IN: {session['user']}")
-        return redirect("/", code=302)
-
-    form = request.form
-    email = form.get("email").strip()
-    password = form.get("password").strip()
-    if email == "" or password == "":
-        flash("You must provide the email and password!", "alert-error")
-        return redirect("/", code=302)
-
-    with db.connection(AUTH_DB) as conn:
-        user = user_by_email(conn, email).maybe(False, lambda usr: usr)
-        if user and valid_login(conn, user, password):
-            session["user"] = user
-            return jsonify({
-                "user_id": user.user_id,
-                "email": user.email,
-                "name": user.name
-            }), 200
-
-    return jsonify({
-        "message": "Could not login. Invalid 'email' or 'password'.",
-        "type": "authentication-error"
-    }), 401
diff --git a/gn3/auth/authentication/users.py b/gn3/auth/authentication/users.py
index 11deba2..6ec6bca 100644
--- a/gn3/auth/authentication/users.py
+++ b/gn3/auth/authentication/users.py
@@ -2,6 +2,7 @@
 from uuid import UUID
 from typing import NamedTuple
 
+import bcrypt
 from pymonad.maybe import Just, Maybe, Nothing
 
 from gn3.auth import db
@@ -17,6 +18,7 @@ class User(NamedTuple):
         return self.user_id
 
 def user_by_email(conn: db.DbConnection, email: str) -> Maybe:
+    """Retrieve user from database by their email address"""
     with db.cursor(conn) as cursor:
         cursor.execute("SELECT * FROM users WHERE email=?", (email,))
         row = cursor.fetchone()
@@ -25,3 +27,29 @@ def user_by_email(conn: db.DbConnection, email: str) -> Maybe:
         return Just(User(UUID(row["user_id"]), row["email"], row["name"]))
 
     return Nothing
+
+def user_by_id(conn: db.DbConnection, user_id: UUID) -> Maybe:
+    """Retrieve user from database by their user id"""
+    with db.cursor(conn) as cursor:
+        cursor.execute("SELECT * FROM users WHERE user_id=?", (str(user_id),))
+        row = cursor.fetchone()
+
+    if row:
+        return Just(User(UUID(row["user_id"]), row["email"], row["name"]))
+
+    return Nothing
+
+def valid_login(conn: db.DbConnection, user: User, password: str) -> bool:
+    """Check the validity of the provided credentials for login."""
+    with db.cursor(conn) as cursor:
+        cursor.execute(
+            ("SELECT * FROM users LEFT JOIN user_credentials "
+             "ON users.user_id=user_credentials.user_id "
+             "WHERE users.user_id=?"),
+            (str(user.user_id),))
+        row = cursor.fetchone()
+
+    if row is None:
+        return False
+
+    return bcrypt.checkpw(password.encode("utf-8"), row["password"])