what openssl function to call for openssl cmd in c?

Question

https://testnet.binance.vision/

bottom of it has the following :

# Sign the request:
timestamp=$(date +%s000)
api_params_with_timestamp="$API_PARAMS&timestamp=$timestamp"
signature=$(echo -n "$api_params_with_timestamp" \
            | openssl dgst -sha256 -sign "$PRIVATE_KEY_PATH" \
            | openssl enc -base64 -A)

I like to do signature sha256 sign with openssl function call in my c source, but I can not figure out how , is there any document that I can refer to ?!