gotosocial/vendor/github.com/go-fed/httpsig/README.md

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# httpsig
`go get github.com/go-fed/httpsig`
Implementation of [HTTP Signatures](https://tools.ietf.org/html/draft-cavage-http-signatures).
Supports many different combinations of MAC, HMAC signing of hash, or RSA
signing of hash schemes. Its goals are:
* Have a very simple interface for signing and validating
* Support a variety of signing algorithms and combinations
* Support setting either headers (`Authorization` or `Signature`)
* Remaining flexible with headers included in the signing string
* Support both HTTP requests and responses
* Explicitly not support known-cryptographically weak algorithms
* Support automatic signing and validating Digest headers
## How to use
`import "github.com/go-fed/httpsig"`
### Signing
Signing a request or response requires creating a new `Signer` and using it:
```
func sign(privateKey crypto.PrivateKey, pubKeyId string, r *http.Request) error {
prefs := []httpsig.Algorithm{httpsig.RSA_SHA512, httpsig.RSA_SHA256}
digestAlgorithm := DigestSha256
// The "Date" and "Digest" headers must already be set on r, as well as r.URL.
headersToSign := []string{httpsig.RequestTarget, "date", "digest"}
signer, chosenAlgo, err := httpsig.NewSigner(prefs, digestAlgorithm, headersToSign, httpsig.Signature)
if err != nil {
return err
}
// To sign the digest, we need to give the signer a copy of the body...
// ...but it is optional, no digest will be signed if given "nil"
body := ...
// If r were a http.ResponseWriter, call SignResponse instead.
return signer.SignRequest(privateKey, pubKeyId, r, body)
}
```
`Signer`s are not safe for concurrent use by goroutines, so be sure to guard
access:
```
type server struct {
signer httpsig.Signer
mu *sync.Mutex
}
func (s *server) handlerFunc(w http.ResponseWriter, r *http.Request) {
privateKey := ...
pubKeyId := ...
// Set headers and such on w
s.mu.Lock()
defer s.mu.Unlock()
// To sign the digest, we need to give the signer a copy of the response body...
// ...but it is optional, no digest will be signed if given "nil"
body := ...
err := s.signer.SignResponse(privateKey, pubKeyId, w, body)
if err != nil {
...
}
...
}
```
The `pubKeyId` will be used at verification time.
### Verifying
Verifying requires an application to use the `pubKeyId` to both retrieve the key
needed for verification as well as determine the algorithm to use. Use a
`Verifier`:
```
func verify(r *http.Request) error {
verifier, err := httpsig.NewVerifier(r)
if err != nil {
return err
}
pubKeyId := verifier.KeyId()
var algo httpsig.Algorithm = ...
var pubKey crypto.PublicKey = ...
// The verifier will verify the Digest in addition to the HTTP signature
return verifier.Verify(pubKey, algo)
}
```
`Verifier`s are not safe for concurrent use by goroutines, but since they are
constructed on a per-request or per-response basis it should not be a common
restriction.