Analyzing the Security Implications of a Client-Side API Proxy Web Application

Introduction

Developing web applications that interact directly with third-party APIs is a common practice, especially when aiming to create lightweight, serverless solutions. However, such architectures can introduce subtle security considerations. This article explores the potential risks and best practices associated with a web application designed to facilitate direct access to an external, public-tier API, where users input their own API keys.

Scenario Overview

Consider a single-page web application (SPA) that enables users to access data from a third-party API. The API provides information like currency exchange rates or global temperatures—data that is already publicly accessible. The API key management involves users obtaining their own keys directly from the third-party provider. Upon visiting the web app:

• Users generate or acquire their API key from the provider.
• They input their API key into the web app interface.
• The app, through JavaScript executed within the browser, makes requests to the third-party API, handles pagination, and displays results in a tabular format.

Key Architectural Details

• No backend server: all API interactions happen client-side.
• Open CORS policy: the API allows requests from any origin.
• User-supplied API keys: each user manages their own access credentials.
• Privacy policy disclosure: the app states that traffic is directly between the user’s browser and the third-party API.

Potential Security and Privacy Concerns

While this architecture offers simplicity and ease of deployment, several security implications merit consideration:

1. Exposure of API Keys:

2. Since the API keys are entered directly into the client-side interface and stored in browser storage (such as sessionStorage), they are inherently accessible to the user.

3. Users can view and extract their own keys using browser developer tools, which is expected and acceptable if the intent is for users to control their credentials.

4. Risk of Key Leakage:

5. If a malicious actor gains access to a user’s browser or device, they could potentially retrieve the stored API key.

6. However, with user awareness and control, this risk is primarily on the individual user rather than the service provider.

7. Third-Party API Usage Limits and Abuse:

8. If multiple users input their own API keys, the provider’s rate limits and quotas may be exceeded or abused, especially if users share or expose their keys publicly.

9. Additionally, if the keys are intended for personal use, exposing them in a shared environment or