By the way if I send with curl
curl -v -d "@ct_precert.json"
http://localhost:6962/ct/v1/add-pre-chain > ct_precert.resp
I got a valid response:
{
"timestamp" : 1524050734816,
"extensions" : "",
"sct_version" : 0,
"id" : "c/Aeof+ZlSf0qH8BriHDBop85+YyHkNy9CKSfIPyzkw=",
"signature" : "BAMARjBEAiBLbXf9MiRtC1CHsSRhrDTxAC2ft+GF3Q6LS1usR9dHlwIgd1sSsQR5jpYCG6kcZclaIAhD6AGJLkS4/dIAmtqWRAk="