Kong HMAC Plugin : Can't replicate signature

I tried to implement HMAC plugin on Kong using steps on konghub

Plugin installed on kong, and I’m trying to hit it, but my signature always failed. Then I try to validate my algorithm using Kong example on documentation (alice123 with key secret)
However I can’t get the same signature as in plugin. Am I did something wrong?

From the example

  signing_string="date: Thu, 22 Jun 2017 17:15:21 GMT\nGET /requests HTTP/1.1"
  digest=HMAC-SHA256(<signing_string>, "secret")

Final signature from Kong example is ujWCGHeec9Xd6UD2zlyxiNMCiXnDOWeVFMu5VeRUxtw=

My algorithm (checked it against few HMAC online tools + base64 encode online) give this result fro Kong example. This match with online tools but not with Kong example

Base64 : Sf6cEUMuDNgm4gbdOD7uSZkLUcsaSdD+4SQrIe5jFTQ=

What’s wrong with my algorithm?