# Base64URL Namespace for URL-safe unpadded Base64 encoding (base64url). ``` enum Base64URL ``` ## Overview `Base64URL` implements the URL-safe, unpadded alphabet defined in [RFC 4648 §5](https://datatracker.ietf.org/doc/html/rfc4648#section-5). The alphabet swaps `+` for `-` and `/` for `_` relative to standard Base64, and strips the trailing `=` padding — producing strings that can be embedded directly in URLs, HTTP headers, JSON values, and filename segments without further escaping. This encoding is the canonical transport form for JOSE (JWS per [RFC 7515](https://datatracker.ietf.org/doc/html/rfc7515) and JWT per [RFC 7519](https://datatracker.ietf.org/doc/html/rfc7519)), [WebAuthn](https://www.w3.org/TR/webauthn-3/) credential blobs, [Nostr NIP-19](https://github.com/nostr-protocol/nips/blob/master/19.md) identifiers, and DID documents. The namespace is caseless; call [`encode(_:)`](/documentation/OpenSSL/Base64URL/encode(_:)) and [`decode(_:)`](/documentation/OpenSSL/Base64URL/decode(_:)) as `static` entry points. > Note: This namespace is pure Swift on top of Foundation’s > `Data(base64Encoded:)` / `base64EncodedString()`. It does **not** > call into `libcrypto` and is not constant-time — do not feed it > secret-dependent material that needs side-channel resistance. > SeeAlso: ``doc://OpenSSL/documentation/OpenSSL/Base64URL/encode(_:)``, ``doc://OpenSSL/documentation/OpenSSL/Base64URL/decode(_:)``