Concat concatenates the args into a single string, substituting previously defined headers if available.

Now returns the number of seconds since the Unix epoch.

PostFormURLEncoded sends an HTTP POST request to a given URL with the data provided, returning either the whole response body or a specified JSON element.

SignStringRS256PKCS8 constructs a string from given args (delimited by newlines), signing it with the (possibly passphrase-encrypted) PKCS #8 private key, and returns the signature in base64.