feat: reddit social sign on (#805)

docs/content/docs/authentication/reddit.mdx

@@ -0,0 +1,81 @@
+---
+title: Reddit
+description: Reddit provider setup and usage.
+---
+
+<Steps>
+    <Step> 
+        ### Get your Reddit Credentials
+        To use Reddit sign in, you need a client ID and client secret. You can get them from the [Reddit Developer Portal](https://www.reddit.com/prefs/apps).
+
+        1. Click "Create App" or "Create Another App"
+        2. Select "web app" as the application type
+        3. Set the redirect URL to `http://localhost:3000/api/auth/callback/reddit` for local development
+        4. For production, set it to your application's domain (e.g. `https://example.com/api/auth/callback/reddit`)
+        5. After creating the app, you'll get the client ID (under the app name) and client secret
+
+        If you change the base path of the auth routes, make sure to update the redirect URL accordingly.
+    </Step>
+
+    <Step>
+        ### Configure the provider
+        To configure the provider, you need to import the provider and pass it to the `socialProviders` option of the auth instance.
+
+        ```ts title="auth.ts"
+        import { betterAuth } from "better-auth"
+        
+        export const auth = betterAuth({
+            socialProviders: {
+                reddit: {
+                    clientId: process.env.REDDIT_CLIENT_ID as string,
+                    clientSecret: process.env.REDDIT_CLIENT_SECRET as string,
+                },
+            },
+        })
+        ```
+    </Step>
+
+    <Step>
+        ### Sign In with Reddit
+        To sign in with Reddit, you can use the `signIn.social` function provided by the client. The `signIn` function takes an object with the following properties:
+        - `provider`: The provider to use. It should be set to `reddit`.
+
+        ```ts title="auth-client.ts"
+        import { createAuthClient } from "better-auth/client"
+        const authClient = createAuthClient()
+        
+        const signIn = async () => {
+            const data = await authClient.signIn.social({
+                provider: "reddit"
+            })
+        }
+        ```
+    </Step>
+</Steps>
+
+## Additional Configuration
+
+### Scopes
+By default, Reddit provides basic user information. If you need additional permissions, you can specify scopes in your auth configuration:
+
+```ts title="auth.ts"
+export const auth = betterAuth({
+    socialProviders: {
+        reddit: {
+            clientId: process.env.REDDIT_CLIENT_ID as string,
+            clientSecret: process.env.REDDIT_CLIENT_SECRET as string,
+            duration: "permanent",
+            scopes: ["identity", "read", "submit"] // Add required scopes
+        },
+    },
+})
+```
+
+Common Reddit scopes include:
+- `identity`: Access basic account information
+- `read`: Access posts and comments
+- `submit`: Submit posts and comments
+- `subscribe`: Manage subreddit subscriptions
+- `history`: Access voting history
+
+For a complete list of available scopes, refer to the [Reddit OAuth2 documentation](https://www.reddit.com/dev/api/oauth).