Base64
Base64 helpers come bundled in crow::utility. Use them for HTTP basic auth headers, embedded images, signed cookies, and similar tasks.
Encoding
#include "crow/utility.h"
std::string encoded = crow::utility::base64encode("Ada Lovelace", 12);
// encoded == "QWRhIExvdmVsYWNl"
Decoding
std::string decoded = crow::utility::base64decode(encoded, encoded.size());
Both functions are pure and allocate; they're fine to call inside handlers but reach for an arena allocator if you process megabytes per request.