Implement Initial Setup for Google OAuth

backend/.env.example

@@ -20,3 +20,6 @@ DJANGO_SENTRY_DSN=None
 DJANGO_SLACK_BOT_TOKEN=None
 DJANGO_SLACK_SIGNING_SECRET=None
 GITHUB_TOKEN=None
+GOOGLE_AUTH_CLIENT_ID=None
+GOOGLE_AUTH_CLIENT_SECRET=None
+GOOGLE_AUTH_REDIRECT_URI=http://localhost:8000/integrations/slack/oauth2/callback/

backend/apps/slack/migrations/0019_googleauth.py

@@ -0,0 +1,39 @@
+# Generated by Django 5.2.4 on 2025-08-11 04:45
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("slack", "0018_conversation_sync_messages"),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name="GoogleAuth",
+            fields=[
+                (
+                    "id",
+                    models.BigAutoField(
+                        auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+                    ),
+                ),
+                ("access_token", models.TextField(blank=True, verbose_name="Access Token")),
+                ("refresh_token", models.TextField(blank=True, verbose_name="Refresh Token")),
+                (
+                    "expires_at",
+                    models.DateTimeField(blank=True, null=True, verbose_name="Token Expiry"),
+                ),
+                (
+                    "member",
+                    models.OneToOneField(
+                        on_delete=django.db.models.deletion.CASCADE,
+                        related_name="google_auth",
+                        to="slack.member",
+                        verbose_name="Slack Member",
+                    ),
+                ),
+            ],
+        ),
+    ]

backend/apps/slack/models/__init__.py

@@ -1,5 +1,6 @@
 from .conversation import Conversation
 from .event import Event
+from .google_auth import GoogleAuth
 from .member import Member
 from .message import Message
 from .workspace import Workspace

backend/apps/slack/models/google_auth.py

@@ -0,0 +1,107 @@
+"""Slack Google OAuth Authentication Model."""
+
+from django.conf import settings
+from django.db import models
+from django.utils import timezone
+from google_auth_oauthlib.flow import Flow
+
+AUTH_ERROR_MESSAGE = (
+    "Google OAuth client ID, secret, and redirect URI must be set in environment variables."
+)
+
+
+class GoogleAuth(models.Model):
+    """Model to store Google OAuth tokens for Slack integration."""
+
+    member = models.OneToOneField(
+        "slack.Member",
+        on_delete=models.CASCADE,
+        related_name="google_auth",
+        verbose_name="Slack Member",
+    )
+    access_token = models.TextField(
+        verbose_name="Access Token",
+        blank=True,
+    )
+    refresh_token = models.TextField(
+        verbose_name="Refresh Token",
+        blank=True,
+    )
+    expires_at = models.DateTimeField(
+        verbose_name="Token Expiry",
+        blank=True,
+        null=True,
+    )
+
+    @staticmethod
+    def get_flow():
+        """Create a Google OAuth flow instance."""
+        if not settings.IS_GOOGLE_AUTH_ENABLED:
+            raise ValueError(AUTH_ERROR_MESSAGE)
+        return Flow.from_client_config(
+            client_config={
+                "web": {
+                    "client_id": settings.GOOGLE_AUTH_CLIENT_ID,
+                    "client_secret": settings.GOOGLE_AUTH_CLIENT_SECRET,
+                    "redirect_uris": [settings.GOOGLE_AUTH_REDIRECT_URI],
+                    "auth_uri": "https://accounts.google.com/o/oauth2/auth",
+                    "token_uri": "https://oauth2.googleapis.com/token",
+                }
+            },
+            scopes=["https://www.googleapis.com/auth/calendar.readonly"],
+        )
+
+    @staticmethod
+    def authenticate(auth_url, member):
+        """Authenticate a member and return a GoogleAuth instance."""
+        if not settings.IS_GOOGLE_AUTH_ENABLED:
+            raise ValueError(AUTH_ERROR_MESSAGE)
+        auth = GoogleAuth.objects.get_or_create(member=member)[0]
+        if auth.access_token and not auth.is_token_expired:
+            return auth
+        if auth.access_token:
+            # If the access token is present but expired, refresh it
+            GoogleAuth.refresh_access_token(auth)
+            return auth
+        # This is the first time authentication, so we need to fetch a new token
+        flow = GoogleAuth.get_flow()
+        flow.redirect_uri = settings.GOOGLE_AUTH_REDIRECT_URI
+        flow.fetch_token(authorization_response=auth_url)
+        auth.access_token = flow.credentials.token
+        auth.refresh_token = flow.credentials.refresh_token
+        auth.expires_at = flow.credentials.expiry
+        auth.save()
+        return auth
+
+    @property
+    def is_token_expired(self):
+        """Check if the access token is expired."""
+        return self.expires_at is None or self.expires_at <= timezone.now() + timezone.timedelta(
+            seconds=60
+        )
+
+    @staticmethod
+    def refresh_access_token(auth):
+        """Refresh the access token using the refresh token."""
+        if not settings.IS_GOOGLE_AUTH_ENABLED:
+            raise ValueError(AUTH_ERROR_MESSAGE)
+        refresh_error = "Google OAuth refresh token is not set or expired."
+        if not auth.refresh_token:
+            raise ValueError(refresh_error)
+
+        flow = GoogleAuth.get_flow()
+        flow.fetch_token(
+            refresh_token=auth.refresh_token,
+            client_id=settings.GOOGLE_AUTH_CLIENT_ID,
+            client_secret=settings.GOOGLE_AUTH_CLIENT_SECRET,
+        )
+
+        credentials = flow.credentials
+        auth.access_token = credentials.token
+        auth.refresh_token = credentials.refresh_token
+        auth.expires_at = credentials.expiry
+        auth.save()
+
+    def __str__(self):
+        """Return a string representation of the GoogleAuth instance."""
+        return f"GoogleAuth(member={self.member})"