A simple approach to convert strings from and to base64. Header only library.
#include "base64.hpp"
#include <iostream>
int main() {
auto base64= to_base64("Hello, World!");
std::cout << base64 << '\n'; // SGVsbG8sIFdvcmxkIQ==
auto s = from_base64("SGVsbG8sIFdvcmxkIQ==");
std::cout << s << '\n'; // Hello, World!
}