crypto: cast oaepLabel to unsigned char*

[codebytere]

This PR fixes an incompatibility between BoringSSL and OpenSSL in compilation through Electron.

OpenSSL has the signature

int EVP_PKEY_CTX_set0_rsa_oaep_label(EVP_PKEY_CTX *ctx, unsigned char *label, int len); 

whereas BoringSSL has:

int EVP_PKEY_CTX_set0_rsa_oaep_label(EVP_PKEY_CTX *ctx, uint8_t *label, size_t label_len); 

Changing this in BoringSSL would not have the correct effect, since label (as returned by OpenSSL_memdup) is a void* & C++ doesn't cast from void* to T* without an explicit cast. OpenSSL has a lot of functions/macros that aren't typesafe which means we don't get the usual C++ type-checking and so this fails to compile without this patch.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines

[davidben]

Correction: this doesn't have anything to do with those signatures. We required unsigned char and uint8_t to be the same type, and it is true in every platform I'm aware of. The signatures are identical.

Rather it's that OpenSSL doesn't use any type signature at all. It's documented with that signature, but it's really a macro without any type-checking. The cast is needed to conform Node to the OpenSSL's documentation because C++ does not implicitly cast void*.

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/27600/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/27620/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/27672/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/27673/

[codebytere]

Landed in cb76f27.