If the custom link is https://example.com/file.php?f=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9 , you can use a URL decoder to reveal the underlying file path. 2. Base64 Decoding Base64 encoding is a common technique used to obfuscate data in URLs. You can use online tools or programming libraries (like Python's base64 module) to decode Base64-encoded strings.