Base64Url encode is not unique to KeyVault and should be in Azure Core

[ahsonkhan]

Base64Url encoding and decoding operation is a very common transformation API. It should be in Azure Core since we know future services will need it.

It is currently internal within KeyVault Common. If we are happy with the design, we should consider making it public and moving it to core.

azure-sdk-for-cpp/sdk/keyvault/azure-security-keyvault-common/inc/azure/keyvault/common/internal/base64url.hpp

Lines 16 to 22 in 0874e1c

	namespace Azure { namespace Security { namespace KeyVault { namespace _internal {
	/**
	* @brief Provides conversion methods for Base64URL.
	*
	*/
	struct Base64Url final

azure-sdk-for-cpp/sdk/core/azure-core/inc/azure/core/base64.hpp

Lines 15 to 21 in 0874e1c

	namespace Azure { namespace Core {
	/**
	* @brief Used to convert one form of data into another, for example encoding binary data into
	* Base64 text.
	*/
	class Convert final {

https://github.com/Azure/azure-sdk-for-net/search?q=base64url
WebPubSub, Attestation, ContainerRegistry, ACS, etc.

cc @JeffreyRichter, @RickWinter, @vhvb1989

[JeffreyRichter]

As always making things public comes with a huge cost (making it general purpose [not just for our specific needs], documentation, samples, support in perpetuity). So, we should avoid this unless there is real customer benefit.

[ahsonkhan]

Leave it internal, but move it to core.