core: Add utilities for generating SHA256 hashes.

[haiqi96]

Description

The PR introduces a hash_utils.cpp/hpp to generate SHA256 hashes and two simple unit tests.
The PR also remove the CMakefile for Openssl. The file was originally added to fix a bug for Cmake with version < 3.16.0. since the minimum version of CMake we are using is 3.16.2, we can safely remove the file and bumb up the required version of cmake.

Validation performed

Generate a presigned url with s3 https url with the hash utils and confirmed that the presigned url works

[kirkrodrigues]

Suggested change

	auto const openssl_err = ERR_get_error();
	return {ERR_error_string(openssl_err, nullptr)};
	auto const openssl_err = ERR_get_error();
	auto* openssl_err_str = ERR_error_string(openssl_err, nullptr);
	if (nullptr == openssl_err_str) {
	return {};
	}
	return {openssl_err_str};

Because ERR_error_string may return nullptr and std::string{nullptr} triggers undefined behaviour.

[haiqi96]

Thanks for catching this. In the nullptr case, should we return some customzied error message so users don't get a "" which could be quite confusing?

[kirkrodrigues]

Uh, we could. The reason I chose {} is because if you call this method and no error had occurred, then you would also get nullptr. So perhaps we should do, in order:

• 0 == openssl_err => {}
• nullptr == openssl_err_str => {"Unknown error"}
• else => {openssl_err_str}

[kirkrodrigues]

Sorry, on no error, ERR_error_string does return a string. So I guess we can just do the last two bullets.

[haiqi96]

never thought someone will try to call this when there's no error, lol. Sure, sounds fair

[kirkrodrigues]

Perhaps to be clearer, we can use "Error has no string representation" instead of "Unknown error".

[haiqi96]

how about
"Error has no string representation, error_code: " + std::to_string(openssl_err)?

[kirkrodrigues]

Sg

[kirkrodrigues]

For the PR title, how about:

core: Add utilities for generating SHA256 hashes.

[haiqi96]

For the PR title, how about:

core: Add utilities for generating SHA256 hashes.

[haiqi96]

For the PR title, how about:

core: Add utilities for generating SHA256 hashes.

Sounds good