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src/routes/private/api/google/auth/check/+server.ts

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+import { json } from '@sveltejs/kit';
+import { getAuthenticatedClient } from '$lib/google/auth/server';
+
+/**
+ * @description Verify the validity of a Google refresh token
+ * @method POST
+ * @param {Request} request
+ * @returns {Response}
+ */
+export async function POST({ request }: { request: Request }): Promise<Response> {
+	try {
+		const { refreshToken } = await request.json();
+
+		if (!refreshToken) {
+			return json({ error: 'Refresh token is required' }, { status: 400 });
+		}
+
+		// Get an authenticated client. This will attempt to get a new access token,
+		// which effectively validates the refresh token.
+		const oauth2Client = getAuthenticatedClient(refreshToken);
+
+		// Attempt to get a new access token
+		await oauth2Client.getAccessToken();
+
+		// If no error is thrown, the token is valid
+		return json({ success: true });
+	} catch (error) {
+		console.error('Failed to verify Google refresh token:', error);
+		// The token is likely invalid or revoked
+		return json({ error: 'Invalid or expired refresh token' }, { status: 401 });
+	}
+}