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httpsign.go
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httpsign.go
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// Copyright 2022 The Gitea Authors. All rights reserved.
// Use of this source code is governed by a MIT-style
// license that can be found in the LICENSE file.
package gitea
import (
"crypto"
"encoding/base64"
"fmt"
"io"
"net/http"
"os"
"strings"
"time"
"github.com/go-fed/httpsig"
"golang.org/x/crypto/ssh"
)
// HTTPSign contains the signer used for signing requests
type HTTPSign struct {
ssh.Signer
cert bool
}
// HTTPSignConfig contains the configuration for creating a HTTPSign
type HTTPSignConfig struct {
fingerprint string
principal string
pubkey bool
cert bool
sshKey string
passphrase string
}
// NewHTTPSignWithPubkey can be used to create a HTTPSign with a public key
// if no fingerprint is specified it returns the first public key found
func NewHTTPSignWithPubkey(fingerprint, sshKey, passphrase string) (*HTTPSign, error) {
return newHTTPSign(&HTTPSignConfig{
fingerprint: fingerprint,
pubkey: true,
sshKey: sshKey,
passphrase: passphrase,
})
}
// NewHTTPSignWithCert can be used to create a HTTPSign with a certificate
// if no principal is specified it returns the first certificate found
func NewHTTPSignWithCert(principal, sshKey, passphrase string) (*HTTPSign, error) {
return newHTTPSign(&HTTPSignConfig{
principal: principal,
cert: true,
sshKey: sshKey,
passphrase: passphrase,
})
}
// NewHTTPSign returns a new HTTPSign
// It will check the ssh-agent or a local file is config.sshKey is set.
// Depending on the configuration it will either use a certificate or a public key
func newHTTPSign(config *HTTPSignConfig) (*HTTPSign, error) {
var signer ssh.Signer
if config.sshKey != "" {
priv, err := os.ReadFile(config.sshKey)
if err != nil {
return nil, err
}
if config.passphrase == "" {
signer, err = ssh.ParsePrivateKey(priv)
if err != nil {
return nil, err
}
} else {
signer, err = ssh.ParsePrivateKeyWithPassphrase(priv, []byte(config.passphrase))
if err != nil {
return nil, err
}
}
if config.cert {
certbytes, err := os.ReadFile(config.sshKey + "-cert.pub")
if err != nil {
return nil, err
}
pub, _, _, _, err := ssh.ParseAuthorizedKey(certbytes)
if err != nil {
return nil, err
}
cert, ok := pub.(*ssh.Certificate)
if !ok {
return nil, fmt.Errorf("failed to parse certificate")
}
signer, err = ssh.NewCertSigner(cert, signer)
if err != nil {
return nil, err
}
}
} else {
// if no sshKey is specified, check if we have a ssh-agent and use it
agent, err := GetAgent()
if err != nil {
return nil, err
}
signers, err := agent.Signers()
if err != nil {
return nil, err
}
if len(signers) == 0 {
return nil, fmt.Errorf("no signers found")
}
if config.cert {
signer = findCertSigner(signers, config.principal)
if signer == nil {
return nil, fmt.Errorf("no certificate found for %s", config.principal)
}
}
if config.pubkey {
signer = findPubkeySigner(signers, config.fingerprint)
if signer == nil {
return nil, fmt.Errorf("no public key found for %s", config.fingerprint)
}
}
}
return &HTTPSign{
Signer: signer,
cert: config.cert,
}, nil
}
// SignRequest signs a HTTP request
func (c *Client) SignRequest(r *http.Request) error {
var contents []byte
headersToSign := []string{httpsig.RequestTarget, "(created)", "(expires)"}
if c.httpsigner.cert {
// add our certificate to the headers to sign
pubkey, _ := ssh.ParsePublicKey(c.httpsigner.Signer.PublicKey().Marshal())
if cert, ok := pubkey.(*ssh.Certificate); ok {
certString := base64.RawStdEncoding.EncodeToString(cert.Marshal())
r.Header.Add("x-ssh-certificate", certString)
headersToSign = append(headersToSign, "x-ssh-certificate")
} else {
return fmt.Errorf("no ssh certificate found")
}
}
// if we have a body, the Digest header will be added and we'll include this also in
// our signature.
if r.Body != nil {
body, err := r.GetBody()
if err != nil {
return fmt.Errorf("getBody() failed: %s", err)
}
contents, err = io.ReadAll(body)
if err != nil {
return fmt.Errorf("failed reading body: %s", err)
}
headersToSign = append(headersToSign, "Digest")
}
// create a signer for the request and headers, the signature will be valid for 10 seconds
signer, _, err := httpsig.NewSSHSigner(c.httpsigner.Signer, httpsig.DigestSha512, headersToSign, httpsig.Signature, 10)
if err != nil {
return fmt.Errorf("httpsig.NewSSHSigner failed: %s", err)
}
// sign the request, use the fingerprint if we don't have a certificate
keyID := "gitea"
if !c.httpsigner.cert {
keyID = ssh.FingerprintSHA256(c.httpsigner.Signer.PublicKey())
}
err = signer.SignRequest(keyID, r, contents)
if err != nil {
return fmt.Errorf("httpsig.Signrequest failed: %s", err)
}
return nil
}
// findCertSigner returns the Signer containing a valid certificate
// if no principal is specified it returns the first certificate found
func findCertSigner(sshsigners []ssh.Signer, principal string) ssh.Signer {
for _, s := range sshsigners {
// Check if the key is a certificate
if !strings.Contains(s.PublicKey().Type(), "cert-v01@openssh.com") {
continue
}
// convert the ssh.Signer to a ssh.Certificate
mpubkey, _ := ssh.ParsePublicKey(s.PublicKey().Marshal())
cryptopub := mpubkey.(crypto.PublicKey)
cert := cryptopub.(*ssh.Certificate)
t := time.Unix(int64(cert.ValidBefore), 0)
// make sure the certificate is at least 10 seconds valid
if time.Until(t) <= time.Second*10 {
continue
}
if principal == "" {
return s
}
for _, p := range cert.ValidPrincipals {
if p == principal {
return s
}
}
}
return nil
}
// findPubkeySigner returns the Signer containing a valid public key
// if no fingerprint is specified it returns the first public key found
func findPubkeySigner(sshsigners []ssh.Signer, fingerprint string) ssh.Signer {
for _, s := range sshsigners {
// Check if the key is a certificate
if strings.Contains(s.PublicKey().Type(), "cert-v01@openssh.com") {
continue
}
if fingerprint == "" {
return s
}
if strings.TrimSpace(string(ssh.MarshalAuthorizedKey(s.PublicKey()))) == fingerprint {
return s
}
if ssh.FingerprintSHA256(s.PublicKey()) == fingerprint {
return s
}
}
return nil
}