Detailed guide to Base64url (RFC 7515 & RFC 4648): why standard Base64 breaks in URLs, character replacements (+ to - and / to _), unpadded strings, and JWT implementations.
Frequently Asked Questions
Q1. Why does standard Base64 break in URL query parameters?
In URL query parameters, "+" represents a whitespace space character, and "/" indicates a path separator, corrupting the original Base64 payload.
Q2. How do I decode Base64url in JavaScript?
Replace - with +, _ with /, and add padding = until the string length is divisible by 4, then call atob().