/*
 void hashlib_HMACSha256Init(hmac_ctx *hmac, const uint8_t* key, size_t keylen){
 size_t i;
 uint8_t sum[64] = {0};
 if(keylen > 64){
 hashlib_Sha256Init(&hmac->sha256_ctx);
 hashlib_Sha256Update(&hmac->sha256_ctx, key, keylen);
 hashlib_Sha256Final(&hmac->sha256_ctx, sum);
 keylen = 32;
 }
 else memcpy(sum, key, keylen);
 memset( hmac->ipad, 0x36, 64 );
 memset( hmac->opad, 0x5C, 64 );
 for( i = 0; i < 64; i++ ){
 hmac->ipad[i] ^= sum[i];
 hmac->opad[i] ^= sum[i];
 }
 hashlib_Sha256Init(&hmac->sha256_ctx);
 hashlib_Sha256Update(&hmac->sha256_ctx, hmac->ipad, 64);
 }