To reduce the likelihood of unitentional exposure of taxpayer access tokens or other private information, you’ll need to ensure all access tokens are stored securely.
Chart access tokens are “keys” to sensitive information. You should treat access tokens with the same level of security as you would passwords.

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Secure storage best practices

Storing tokens securely should be done on the backend (server-side) of your application, not on the frontend (client-side). A frontend application is more susceptible to potential security threats such as Cross-Site Scripting (XSS) attacks or unauthorized access if the client is compromised. Therefore, Chart requires developers to store tokens securely on the backend server where you have better control over access and security. No application is 100% secure, but there are ways to reduce the potential of an exposure (and its impact) by following a few best practices:
  1. Store tokens on the backend of your application.
  2. Encrypt the access token before storing it.
  3. Use environment variables or a secure configuration management system to store static sensitive information that needs to be referenced like client_secret.
  4. Never store access tokens in code files or easily accessible directories with human access.
  5. Ensure that tokens are not exposed in URLs, logs, or error messages.
  6. Keep all server-side components, libraries, and frameworks up-to-date with security patches to mitigate potential vulnerabilities.
Determine the best method for securely storing access tokens in your application’s backend. Reference the sections below if you need additional help.

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Encryption

To add an extra layer of security, you can encrypt the access token before storing it. Select a strong symmetric encryption algorithm, such as AES-256. Avoid using weak algorithms like DES, as they are susceptible to brute-force attacks due to its small key size (56 bits).

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Never expose access tokens

Ensure that tokens are not exposed in URLs, log files, or error messages. Regularly review logs for any exposure. Ensure your frontend application never receives the access token to avoid incidental exposure. Your frontend, client-side application should only receive tax data, never the token itself.