ApiAuth-compatible package for signing and verifying HTTP requests in golang.

In order to prevent a security vulnerability present in the reference version of ApiAuth we have added functions in order to sign and verify requests with a canonical string that includes the HTTP method. We have added the fucntions SignWithMethod and CanonicalStringWithMethod, and the Verify function has been modified to accept requests where the request signature matches CanonicalString OR CanonicalStringWithMethod. In the future the old versions will be removed and canonical strings will only be considered a match if they include the request method. We recommend you start using the new way of siging requests immediately.

Signing a request:

import "github.com/pd/apiauth"

req, _ := http.NewRequest("GET", "http://example.com", nil)

// The `Date` header _must_ be present.
// If the request body is set, `Content-Type` and `Content-MD5` must
// also be present.
req.Header.Set("Date", apiauth.Date())

err := apiauth.Sign(req, "access_id", "secret_key")

Verifying a request:

err := apiauth.Verify(req, "secret_key")
if err != nil {
  // Failed.
}

Functions are exposed for the lower-level operations, as well, in case you need more granular control:

// Given a request, returns the `<Content-Type>,<MD5>,<URI>,<Date>` string used for the HMAC.
str := apiauth.CanonicalString(req)

// Given a canonical string and secret key, computes the signature using HMAC-SHA1:
signature := apiauth.Compute(str, "secret_key")

// A helper for generating a RFC1123-formatted date using the current time:
apiauth.Date()

// Or a given time:
t := time.Date(2009, time.November, 10, 23, 0, 0, 0, time.UTC)
apiauth.DateForTime(t)

This implementation is intentionally somewhat less "friendly" than mgomes' Ruby implementation:

• Only the Authorization header is set for you by apiauth.Sign; setting the Date, Content-Type and Content-MD5 headers is the caller's responsibility.
• The apiauth.Verify function does not enforce a maximum time duration between the Date header in a request and the matching Date value computed by the server. Protection against replay attacks is the caller's responsibility. (NB: but maybe shouldn't be; I'm just being lazy right now, as it's already handled in the application I'm writing this for)
• The apiauth.Verify function does not validate the Content-MD5 header: doing so would require reading the entire request body into memory at least once, which is undesirable in many use cases. Verification of the payload MD5 is the caller's responsibility.