Function getTokenExpiration

getTokenExpiration(token: string): null | Date
Extract expiration date from JWT token without verification

Parses the token payload to extract the expiration timestamp ('exp' claim) and converts it to a JavaScript Date object. This function provides expiration information without performing cryptographic verification, making it useful for displaying token validity periods to users or scheduling token refresh.

The function safely handles malformed tokens or missing expiration claims by returning null, allowing calling code to handle these cases appropriately.
Parameters
- token: string
  JWT token string to extract expiration from
Returns null | Date
Date object representing token expiration, or null if extraction fails
Example
```
// Display token expiration to user
const token = 'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...';
const expirationDate = getTokenExpiration(token);

if (expirationDate) {
  console.log(`Token expires at: ${expirationDate.toLocaleString()}`);
  console.log(`Time remaining: ${expirationDate.getTime() - Date.now()}ms`);
} else {
  console.log('Could not determine token expiration');
}
```
Example
```
// Schedule token refresh based on expiration
const expiration = getTokenExpiration(accessToken);
if (expiration) {
  const refreshTime = expiration.getTime() - (5 * 60 * 1000); // 5 minutes before expiry
  setTimeout(refreshTokens, refreshTime - Date.now());
}
```
- Defined in src/shared/utils/auth.ts:579