// Copyright (c) 2021 James Bowes. All rights reserved.

// Use of this source code is governed by a BSD-style

// license that can be found in the LICENSE file.

package httpsig

import (

"bytes"

"crypto/ecdsa"

"crypto/rsa"

"io/ioutil"

"net/http"

"time"

)

var defaultHeaders = []string{"content-type", "content-length"} // also method, path, query, and digest

func sliceHas(haystack []string, needle string) bool {

for _, n := range haystack {

if n == needle {

return true

}

}

return false

}

// NewSignTransport returns a new client transport that wraps the provided transport with

// http message signing and body digest creation.

//

// Use the various `WithSign*` option funcs to configure signature algorithms with their provided

// key ids. You must provide at least one signing option. A signature for every provided key id is

// included on each request. Multiple included signatures allow you to gracefully introduce stronger

// algorithms, rotate keys, etc.

func NewSignTransport(transport http.RoundTripper, opts ...signOption) http.RoundTripper {

s := signer{

keys: map[string]sigHolder{},

nowFunc: time.Now,

}

for _, o := range opts {

o.configureSign(&s)

}

if len(s.headers) == 0 {

s.headers = defaultHeaders[:]

}

// TODO: normalize headers? lowercase & de-dupe

// specialty components and digest first, for aesthetics

for _, comp := range []string{"digest", "@query", "@path", "@method"} {

if !sliceHas(s.headers, comp) {

s.headers = append([]string{comp}, s.headers...)

}

}

return rt(func(r *http.Request) (*http.Response, error) {

nr := r.Clone(r.Context())

b := &bytes.Buffer{}

if r.Body != nil {

n, err := b.ReadFrom(r.Body)

if err != nil {

return nil, err

}

defer r.Body.Close()

if n != 0 {

r.Body = ioutil.NopCloser(bytes.NewReader(b.Bytes()))

}

}

// Always set a digest (for now)

// TODO: we could skip setting digest on an empty body if content-length is included in the sig

nr.Header.Set("Digest", calcDigest(b.Bytes()))

msg := messageFromRequest(nr)

hdr, err := s.Sign(msg)

if err != nil {

return nil, err

}

for k, v := range hdr {

nr.Header[k] = v

}

return transport.RoundTrip(nr)

})

}

type rt func(*http.Request) (*http.Response, error)

func (r rt) RoundTrip(req *http.Request) (*http.Response, error) { return r(req) }

// NewVerifyMiddleware returns a configured http server middleware that can be used to wrap

// multiple handlers for http message signature and digest verification.

//

// Use the `WithVerify*` option funcs to configure signature verification algorithms that map

// to their provided key ids.

//

// Requests with missing signatures, malformed signature headers, expired signatures, or

// invalid signatures are rejected with a `400` response. Only one valid signature is required

// from the known key ids. However, only the first known key id is checked.

func NewVerifyMiddleware(opts ...verifyOption) func(http.Handler) http.Handler {

// TODO: form and multipart support

v := verifier{

keys: make(map[string]verHolder),

nowFunc: time.Now,

}

for _, o := range opts {

o.configureVerify(&v)

}

serveErr := func(rw http.ResponseWriter) {

// TODO: better error and custom error handler

rw.Header().Set("Content-Type", "text/plain")

rw.WriteHeader(http.StatusBadRequest)

_, _ = rw.Write([]byte("invalid required signature"))

}

return func(h http.Handler) http.Handler {

return http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {

msg := messageFromRequest(r)

err := v.Verify(msg)

if err != nil {

serveErr(rw)

return

}

b := &bytes.Buffer{}

if r.Body != nil {

n, err := b.ReadFrom(r.Body)

if err != nil {

serveErr(rw)

return

}

defer r.Body.Close()

if n != 0 {

r.Body = ioutil.NopCloser(bytes.NewReader(b.Bytes()))

}

}

// Check the digest if set. We only support id-sha-256 for now.

// TODO: option to require this?

if dig := r.Header.Get("Digest"); dig != "" {

if !verifyDigest(b.Bytes(), dig) {

serveErr(rw)

}

}

h.ServeHTTP(rw, r)

})

}

}

type signOption interface {

configureSign(s *signer)

}

type verifyOption interface {

configureVerify(v *verifier)

}

type signOrVerifyOption interface {

signOption

verifyOption

}

type optImpl struct {

s func(s *signer)

v func(v *verifier)

}

func (o *optImpl) configureSign(s *signer) { o.s(s) }

func (o *optImpl) configureVerify(v *verifier) { o.v(v) }

// WithHeaders sets the list of headers that will be included in the signature.

// The Digest header is always included (and the digest calculated).

//

// If not provided, the default headers `content-type, content-length, host` are used.

func WithHeaders(hdr ...string) signOption {

// TODO: use this to implement required headers in verify?

return &optImpl{

s: func(s *signer) { s.headers = hdr },

}

}

// WithSignRsaPssSha512 adds signing using `rsa-pss-sha512` with the given private key

// using the given key id.

func WithSignRsaPssSha512(keyID string, pk *rsa.PrivateKey) signOption {

return &optImpl{

s: func(s *signer) { s.keys[keyID] = signRsaPssSha512(pk) },

}

}

// WithVerifyRsaPssSha512 adds signature verification using `rsa-pss-sha512` with the

// given public key using the given key id.

func WithVerifyRsaPssSha512(keyID string, pk *rsa.PublicKey) verifyOption {

return &optImpl{

v: func(v *verifier) { v.keys[keyID] = verifyRsaPssSha512(pk) },

}

}

// WithSignEcdsaP256Sha256 adds signing using `ecdsa-p256-sha256` with the given private key

// using the given key id.

func WithSignEcdsaP256Sha256(keyID string, pk *ecdsa.PrivateKey) signOption {

return &optImpl{

s: func(s *signer) { s.keys[keyID] = signEccP256(pk) },

}

}

// WithVerifyEcdsaP256Sha256 adds signature verification using `ecdsa-p256-sha256` with the

// given public key using the given key id.

func WithVerifyEcdsaP256Sha256(keyID string, pk *ecdsa.PublicKey) verifyOption {

return &optImpl{

v: func(v *verifier) { v.keys[keyID] = verifyEccP256(pk) },

}

}

// WithHmacSha256 adds signing or signature verification using `hmac-sha256` with the

// given shared secret using the given key id.

func WithHmacSha256(keyID string, secret []byte) signOrVerifyOption {

return &optImpl{

s: func(s *signer) { s.keys[keyID] = signHmacSha256(secret) },

v: func(v *verifier) { v.keys[keyID] = verifyHmacSha256(secret) },

}

}