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issuer.go
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issuer.go
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package fleet
import (
"bytes"
"crypto"
"crypto/ed25519"
"crypto/rand"
"crypto/sha256"
"crypto/x509"
"encoding/base64"
"encoding/json"
"fmt"
"io"
"io/fs"
"log/slog"
"net/http"
"os"
"time"
"github.com/KarpelesLab/goupd"
)
func WithIssuer(url string, opts ...AgentOption) *Agent {
// this means that GetFile(internal_key.jwt) and such should call our issuer
//
// Issuer API is a url receiving a POST body containing "ts", "key" and "file"
// - ts is a timestamp in microtime. Not two requests should have the same ts
// - key is a base64url-encoded public key
// - file is the file requested
// additionally, the headers include a "Sec-Body-Signature" value which is the
// signature of the json body encoded in base64url. The issuer must verify the
// signature, should verify additional information (source ip, etc) and decide
// to issue or not the requested file.
return WithGetFile(func(a *Agent, f string) ([]byte, error) {
if f == "internal_key.key" {
// this will result in a loop call when using getLocalKey(), so reject it now
fn, err := findFile(f)
if err == nil {
return os.ReadFile(fn)
}
return nil, fs.ErrNotExist
}
// get local key
key, err := a.getLocalKey()
if err != nil {
return nil, err
}
pubBin, err := x509.MarshalPKIXPublicKey(key.Public())
if err != nil {
return nil, err
}
// fetch our local hostname to be included in request (just informative)
hn, _ := os.Hostname()
body := map[string]any{
"ts": time.Now().UnixMicro(),
"file": f,
"key": base64.RawURLEncoding.EncodeToString(pubBin),
"host": hn,
"goupd": goupd.GetVars(),
}
// prepare request body (will never fail)
bodyBin, _ := json.Marshal(body)
// sign request
// Sign(rand io.Reader, digest []byte, opts SignerOpts) (signature []byte, err error)
var sig []byte
switch key.(type) {
case ed25519.PrivateKey:
// need to not hash
sig, err = key.Sign(rand.Reader, bodyBin, crypto.Hash(0))
default:
h := sha256.Sum256(bodyBin)
sig, err = key.Sign(rand.Reader, h[:], crypto.SHA256)
}
if err != nil {
slog.Error(fmt.Sprintf("error while signing request: %s", err), "event", "fleet:issuer:getfile_sign_fail")
return nil, fmt.Errorf("while signing request: %w", err)
}
//log.Printf("POST to issuer %s: %s", url, bodyBin)
// Pass "sig" in header
req, err := http.NewRequest("POST", url, bytes.NewReader(bodyBin))
if err != nil {
return nil, fmt.Errorf("failed to initate request to issuer: %w", err)
}
req.Header.Set("Sec-Body-Signature", base64.RawURLEncoding.EncodeToString(sig))
req.Header.Set("Content-Type", "application/json")
resp, err := http.DefaultClient.Do(req)
if err != nil {
return nil, fmt.Errorf("while calling issuer: %w", err)
}
defer resp.Body.Close()
if resp.StatusCode != 200 {
return nil, fmt.Errorf("failed to read %s: %s", f, resp.Status)
}
// read body in a buffer
buf := &bytes.Buffer{}
_, err = io.Copy(buf, resp.Body)
if err != nil {
return nil, err
}
return buf.Bytes(), nil
}, opts...)
}