Request body empty after reading it

[kaischwanke]

Bug Report Checklist

• Have you provided a code sample to reproduce the issue?
• Have you tested with the latest release to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?

Description
Reading the request body in the sign function leaves it empty

To Reproduce
Test to illustrate the behaviour:

func TestBodyRestore(t *testing.T) {
	originalBody := "{\"foo\": \"bar\"}"
	getRequest, _ := http.NewRequest("GET", "", strings.NewReader(originalBody))
	bodyHash := getSignedBodyHash(getRequest)
	bodyHash2 := getSignedBodyHash(getRequest)
	if bodyHash != bodyHash2 {
		t.Errorf("Body hashes sould be the same")
	}
}

func getSignedBodyHash(r *http.Request) string {
	signer := &oauth.Signer{ConsumerKey: consumerKey, SigningKey: signingKey}
	_ = signer.Sign(r)
	authHeader := r.Header["Authorization"][0]
	return extractBodyHash(authHeader)
}

func extractBodyHash(input string) string {
	regexPattern := `oauth_body_hash="([^"]+)"`
	re := regexp.MustCompile(regexPattern)

	match := re.FindStringSubmatch(input)
	if len(match) == 0 {
		panic("value not found")
	}
	return match[1]
}

Expected behavior
The request body should remain intact after reading it

Additional context
The request body in Go is a ReadCloser interface. Once you read the content, the buffer will be empty.
I had forgotten about that behaviour in my previous PR

Related issues/PRs
PR #10 created

[danny-gallagher]

Resolved in #10