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remote.go
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remote.go
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package api
import (
"crypto/ed25519"
"encoding/json"
"errors"
"fmt"
"io"
"net/http"
"time"
"github.com/go-chi/render"
"github.com/mr-tron/base58"
"go.hackfix.me/disco/crypto"
"go.hackfix.me/disco/db/models"
dbtypes "go.hackfix.me/disco/db/types"
"go.hackfix.me/disco/web/server/types"
)
// RemoteJoin authenticates a remote Disco node.
// The request is expected to contain an Authorization header with a random
// token encoded as a base 58 string, and its signature. If the token matches an
// existing and valid invitation record, the request body is read, which is
// expected to contain the client's X25519 public key. If successful, ECDH key
// exchange is performed to generate the shared secret key, which is used to
// verify the token signature, and encrypt the generated TLS client certificate
// that is sent in the response.
func (h *Handler) RemoteJoin(w http.ResponseWriter, r *http.Request) {
// Extract the token signature and data from the Authorization header.
tokenBundle := r.Header.Get("Authorization")
tokenSig, tokenData, err := decodeToken(tokenBundle)
if err != nil {
_ = render.Render(w, r, types.ErrUnauthorized("invalid invite token"))
return
}
// Lookup the token in the DB.
inv := &models.Invite{Token: base58.Encode(tokenData)}
if err := inv.Load(h.appCtx.DB.NewContext(), h.appCtx.DB); err != nil {
var errNoRes dbtypes.ErrNoResult
if errors.As(err, &errNoRes) {
_ = render.Render(w, r, types.ErrUnauthorized("invalid invite token"))
return
}
_ = render.Render(w, r, types.ErrBadRequest(err))
return
}
// Read the client's X25519 pubkey from the request body.
clientPubKeyEnc, err := io.ReadAll(r.Body)
if err != nil {
_ = render.Render(w, r, types.ErrBadRequest(err))
return
}
clientPubKeyData, err := base58.Decode(string(clientPubKeyEnc))
if err != nil {
_ = render.Render(w, r, types.ErrBadRequest(err))
return
}
privKey, err := inv.PrivateKey(h.appCtx.User.PrivateKey)
if err != nil {
_ = render.Render(w, r, types.ErrInternal(err))
return
}
// Perform ECDH key exchange to generate the shared secret key.
sharedKey, _, err := crypto.ECDHExchange(clientPubKeyData, privKey.Bytes())
if err != nil {
_ = render.Render(w, r, types.ErrInternal(err))
return
}
// Finally, verify the token signature, using the shared key as a seed.
privSignKey := ed25519.NewKeyFromSeed(sharedKey)
sigVerified := ed25519.Verify(privSignKey.Public().(ed25519.PublicKey),
tokenData, tokenSig)
if !sigVerified {
_ = render.Render(w, r, types.ErrUnauthorized("invalid invite token"))
return
}
// All good, so generate the response payload.
serverCert, serverCertPEM, serverSAN, err := h.appCtx.ServerTLSInfo()
if err != nil {
_ = render.Render(w, r, types.ErrInternal(err))
return
}
clientCert, clientKey, err := crypto.NewTLSCert(
inv.User.Name, []string{serverSAN}, time.Now().Add(24*time.Hour), serverCert,
)
if err != nil {
_ = render.Render(w, r, types.ErrInternal(err))
return
}
payload := &types.RemoteJoinResponsePayload{
TLSCACert: string(serverCertPEM),
TLSServerSAN: serverSAN,
TLSClientCert: clientCert,
TLSClientKey: clientKey,
}
payloadJSON, err := json.Marshal(payload)
if err != nil {
_ = render.Render(w, r, types.ErrInternal(err))
return
}
// Encrypt the payload with shared key.
var sharedKeyArr [32]byte
copy(sharedKeyArr[:], sharedKey)
payloadEnc, err := crypto.EncryptSymInMemory(payloadJSON, &sharedKeyArr)
if err != nil {
_ = render.Render(w, r, types.ErrInternal(err))
return
}
resp := &types.RemoteJoinResponse{
Response: &types.Response{StatusCode: http.StatusOK},
Data: base58.Encode(payloadEnc),
}
_ = render.Render(w, r, resp)
}
func decodeToken(token string) ([]byte, []byte, error) {
tokenDec, err := base58.Decode(token)
if err != nil {
return nil, nil, fmt.Errorf("failed decoding invite token: %w", err)
}
if len(tokenDec) != 96 {
return nil, nil, errors.New("invalid invite token")
}
return tokenDec[:64], tokenDec[64:], nil
}