lib/controller/localdb/container_gateway.go

   1 // Copyright (C) The Arvados Authors. All rights reserved.
   2 //
   3 // SPDX-License-Identifier: AGPL-3.0
   4
   5 package localdb
   6
   7 import (
   8         "bufio"
   9         "bytes"
  10         "context"
  11         "crypto/hmac"
  12         "crypto/sha256"
  13         "crypto/subtle"
  14         "crypto/tls"
  15         "crypto/x509"
  16         "errors"
  17         "fmt"
  18         "io"
  19         "io/ioutil"
  20         "net"
  21         "net/http"
  22         "net/http/httputil"
  23         "net/url"
  24         "strings"
  25
  26         "git.arvados.org/arvados.git/lib/controller/rpc"
  27         "git.arvados.org/arvados.git/lib/service"
  28         "git.arvados.org/arvados.git/lib/webdavfs"
  29         "git.arvados.org/arvados.git/sdk/go/arvados"
  30         "git.arvados.org/arvados.git/sdk/go/auth"
  31         "git.arvados.org/arvados.git/sdk/go/ctxlog"
  32         "git.arvados.org/arvados.git/sdk/go/httpserver"
  33         "github.com/hashicorp/yamux"
  34         "golang.org/x/net/webdav"
  35 )
  36
  37 var (
  38         forceProxyForTest       = false
  39         forceInternalURLForTest *arvados.URL
  40 )
  41
  42 // ContainerLog returns a WebDAV handler that reads logs from the
  43 // indicated container. It works by proxying the request to
  44 //
  45 //   - the container gateway, if the container is running
  46 //
  47 //   - a different controller process, if the container is running and
  48 //     the gateway is accessible through a tunnel to a different
  49 //     controller process
  50 //
  51 //   - keep-web, if saved logs exist and there is no gateway (or the
  52 //     container is finished)
  53 //
  54 //   - an empty-collection stub, if there is no gateway and no saved
  55 //     log
  56 func (conn *Conn) ContainerLog(ctx context.Context, opts arvados.ContainerLogOptions) (http.Handler, error) {
  57         ctr, err := conn.railsProxy.ContainerGet(ctx, arvados.GetOptions{UUID: opts.UUID, Select: []string{"uuid", "state", "gateway_address", "log"}})
  58         if err != nil {
  59                 return nil, err
  60         }
  61         if ctr.GatewayAddress == "" ||
  62                 (ctr.State != arvados.ContainerStateLocked && ctr.State != arvados.ContainerStateRunning) {
  63                 return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
  64                         conn.serveContainerLogViaKeepWeb(opts, ctr, w, r)
  65                 }), nil
  66         }
  67         dial, arpc, err := conn.findGateway(ctx, ctr, opts.NoForward)
  68         if err != nil {
  69                 return nil, err
  70         }
  71         if arpc != nil {
  72                 opts.NoForward = true
  73                 return arpc.ContainerLog(ctx, opts)
  74         }
  75         return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
  76                 r = r.WithContext(ctx)
  77                 var proxyReq *http.Request
  78                 var proxyErr error
  79                 var expectRespondAuth string
  80                 proxy := &httputil.ReverseProxy{
  81                         // Our custom Transport:
  82                         //
  83                         // - Uses a custom dialer to connect to the
  84                         // gateway (either directly or through a
  85                         // tunnel set up though ContainerTunnel)
  86                         //
  87                         // - Verifies the gateway's TLS certificate
  88                         // using X-Arvados-Authorization headers.
  89                         //
  90                         // This involves modifying the outgoing
  91                         // request header in DialTLSContext.
  92                         // (ReverseProxy certainly doesn't expect us
  93                         // to do this, but it works.)
  94                         Transport: &http.Transport{
  95                                 DialTLSContext: func(ctx context.Context, network, addr string) (net.Conn, error) {
  96                                         tlsconn, requestAuth, respondAuth, err := dial()
  97                                         if err != nil {
  98                                                 return nil, err
  99                                         }
 100                                         proxyReq.Header.Set("X-Arvados-Authorization", requestAuth)
 101                                         expectRespondAuth = respondAuth
 102                                         return tlsconn, nil
 103                                 },
 104                         },
 105                         Director: func(r *http.Request) {
 106                                 // Scheme/host of incoming r.URL are
 107                                 // irrelevant now, and may even be
 108                                 // missing. Host is ignored by our
 109                                 // DialTLSContext, but we need a
 110                                 // generic syntactically correct URL
 111                                 // for net/http to work with.
 112                                 r.URL.Scheme = "https"
 113                                 r.URL.Host = "0.0.0.0:0"
 114                                 r.Header.Set("X-Arvados-Container-Gateway-Uuid", opts.UUID)
 115                                 proxyReq = r
 116                         },
 117                         ModifyResponse: func(resp *http.Response) error {
 118                                 if resp.Header.Get("X-Arvados-Authorization-Response") != expectRespondAuth {
 119                                         // Note this is how we detect
 120                                         // an attacker-in-the-middle.
 121                                         return httpserver.ErrorWithStatus(errors.New("bad X-Arvados-Authorization-Response header"), http.StatusBadGateway)
 122                                 }
 123                                 return nil
 124                         },
 125                         ErrorHandler: func(w http.ResponseWriter, r *http.Request, err error) {
 126                                 proxyErr = err
 127                         },
 128                 }
 129                 proxy.ServeHTTP(w, r)
 130                 if proxyErr == nil {
 131                         // proxy succeeded
 132                         return
 133                 }
 134                 // If proxying to the container gateway fails, it
 135                 // might be caused by a race where crunch-run exited
 136                 // after we decided (above) the log was not final.
 137                 // In that case we should proxy to keep-web.
 138                 ctr, err := conn.railsProxy.ContainerGet(ctx, arvados.GetOptions{
 139                         UUID:   opts.UUID,
 140                         Select: []string{"uuid", "state", "gateway_address", "log"},
 141                 })
 142                 if err != nil {
 143                         // Lost access to the container record?
 144                         httpserver.Error(w, "error re-fetching container record: "+err.Error(), http.StatusServiceUnavailable)
 145                 } else if ctr.State == arvados.ContainerStateLocked || ctr.State == arvados.ContainerStateRunning {
 146                         // No race, proxyErr was the best we can do
 147                         httpserver.Error(w, "proxy error: "+proxyErr.Error(), http.StatusServiceUnavailable)
 148                 } else {
 149                         conn.serveContainerLogViaKeepWeb(opts, ctr, w, r)
 150                 }
 151         }), nil
 152 }
 153
 154 // serveContainerLogViaKeepWeb handles a request for saved container
 155 // log content by proxying to one of the configured keep-web servers.
 156 //
 157 // It tries to choose a keep-web server that is running on this host.
 158 func (conn *Conn) serveContainerLogViaKeepWeb(opts arvados.ContainerLogOptions, ctr arvados.Container, w http.ResponseWriter, r *http.Request) {
 159         if ctr.Log == "" {
 160                 // Special case: if no log data exists yet, we serve
 161                 // an empty collection by ourselves instead of
 162                 // proxying to keep-web.
 163                 conn.serveEmptyDir("/arvados/v1/containers/"+ctr.UUID+"/log", w, r)
 164                 return
 165         }
 166         myURL, _ := service.URLFromContext(r.Context())
 167         u := url.URL(myURL)
 168         myHostname := u.Hostname()
 169         var webdavBase arvados.URL
 170         var ok bool
 171         for webdavBase = range conn.cluster.Services.WebDAVDownload.InternalURLs {
 172                 ok = true
 173                 u := url.URL(webdavBase)
 174                 if h := u.Hostname(); h == "127.0.0.1" || h == "0.0.0.0" || h == "::1" || h == myHostname {
 175                         // Prefer a keep-web service running on the
 176                         // same host as us. (If we don't find one, we
 177                         // pick one arbitrarily.)
 178                         break
 179                 }
 180         }
 181         if !ok {
 182                 httpserver.Error(w, "no internalURLs configured for WebDAV service", http.StatusInternalServerError)
 183                 return
 184         }
 185         proxy := &httputil.ReverseProxy{
 186                 Director: func(r *http.Request) {
 187                         r.URL = &url.URL{
 188                                 Scheme: webdavBase.Scheme,
 189                                 Host:   webdavBase.Host,
 190                                 Path:   "/by_id/" + url.PathEscape(ctr.Log) + opts.Path,
 191                         }
 192                         // Our outgoing Host header must match
 193                         // WebDAVDownload.ExternalURL, otherwise
 194                         // keep-web does not accept an auth token.
 195                         r.Host = conn.cluster.Services.WebDAVDownload.ExternalURL.Host
 196                         // We already checked permission on the
 197                         // container, so we can use a root token here
 198                         // instead of counting on the "access to log
 199                         // via container request and container"
 200                         // permission check, which can be racy when a
 201                         // request gets retried with a new container.
 202                         r.Header.Set("Authorization", "Bearer "+conn.cluster.SystemRootToken)
 203                 },
 204         }
 205         if conn.cluster.TLS.Insecure {
 206                 proxy.Transport = &http.Transport{
 207                         TLSClientConfig: &tls.Config{
 208                                 InsecureSkipVerify: conn.cluster.TLS.Insecure,
 209                         },
 210                 }
 211         }
 212         proxy.ServeHTTP(w, r)
 213 }
 214
 215 // serveEmptyDir handles read-only webdav requests as if there was an
 216 // empty collection rooted at the given path. It's equivalent to
 217 // proxying to an empty collection in keep-web, but avoids the extra
 218 // hop.
 219 func (conn *Conn) serveEmptyDir(path string, w http.ResponseWriter, r *http.Request) {
 220         wh := webdav.Handler{
 221                 Prefix:     path,
 222                 FileSystem: webdav.NewMemFS(),
 223                 LockSystem: webdavfs.NoLockSystem,
 224                 Logger: func(r *http.Request, err error) {
 225                         if err != nil {
 226                                 ctxlog.FromContext(r.Context()).WithError(err).Info("webdav error on empty collection fs")
 227                         }
 228                 },
 229         }
 230         wh.ServeHTTP(w, r)
 231 }
 232
 233 // ContainerSSH returns a connection to the SSH server in the
 234 // appropriate crunch-run process on the worker node where the
 235 // specified container is running.
 236 //
 237 // If the returned error is nil, the caller is responsible for closing
 238 // sshconn.Conn.
 239 func (conn *Conn) ContainerSSH(ctx context.Context, opts arvados.ContainerSSHOptions) (sshconn arvados.ConnectionResponse, err error) {
 240         user, err := conn.railsProxy.UserGetCurrent(ctx, arvados.GetOptions{})
 241         if err != nil {
 242                 return sshconn, err
 243         }
 244         ctr, err := conn.railsProxy.ContainerGet(ctx, arvados.GetOptions{UUID: opts.UUID, Select: []string{"uuid", "state", "gateway_address", "interactive_session_started"}})
 245         if err != nil {
 246                 return sshconn, err
 247         }
 248         ctxRoot := auth.NewContext(ctx, &auth.Credentials{Tokens: []string{conn.cluster.SystemRootToken}})
 249         if !user.IsAdmin || !conn.cluster.Containers.ShellAccess.Admin {
 250                 if !conn.cluster.Containers.ShellAccess.User {
 251                         return sshconn, httpserver.ErrorWithStatus(errors.New("shell access is disabled in config"), http.StatusServiceUnavailable)
 252                 }
 253                 crs, err := conn.railsProxy.ContainerRequestList(ctxRoot, arvados.ListOptions{Limit: -1, Filters: []arvados.Filter{{"container_uuid", "=", opts.UUID}}})
 254                 if err != nil {
 255                         return sshconn, err
 256                 }
 257                 for _, cr := range crs.Items {
 258                         if cr.ModifiedByUserUUID != user.UUID {
 259                                 return sshconn, httpserver.ErrorWithStatus(errors.New("permission denied: container is associated with requests submitted by other users"), http.StatusForbidden)
 260                         }
 261                 }
 262                 if crs.ItemsAvailable != len(crs.Items) {
 263                         return sshconn, httpserver.ErrorWithStatus(errors.New("incomplete response while checking permission"), http.StatusInternalServerError)
 264                 }
 265         }
 266
 267         if ctr.State == arvados.ContainerStateQueued || ctr.State == arvados.ContainerStateLocked {
 268                 return sshconn, httpserver.ErrorWithStatus(fmt.Errorf("container is not running yet (state is %q)", ctr.State), http.StatusServiceUnavailable)
 269         } else if ctr.State != arvados.ContainerStateRunning {
 270                 return sshconn, httpserver.ErrorWithStatus(fmt.Errorf("container has ended (state is %q)", ctr.State), http.StatusGone)
 271         }
 272
 273         dial, arpc, err := conn.findGateway(ctx, ctr, opts.NoForward)
 274         if err != nil {
 275                 return sshconn, err
 276         }
 277         if arpc != nil {
 278                 opts.NoForward = true
 279                 return arpc.ContainerSSH(ctx, opts)
 280         }
 281
 282         tlsconn, requestAuth, respondAuth, err := dial()
 283         if err != nil {
 284                 return sshconn, err
 285         }
 286         bufr := bufio.NewReader(tlsconn)
 287         bufw := bufio.NewWriter(tlsconn)
 288
 289         u := url.URL{
 290                 Scheme: "http",
 291                 Host:   tlsconn.RemoteAddr().String(),
 292                 Path:   "/ssh",
 293         }
 294         postform := url.Values{
 295                 // uuid is only needed for older crunch-run versions
 296                 // (current version uses X-Arvados-* header below)
 297                 "uuid":           {opts.UUID},
 298                 "detach_keys":    {opts.DetachKeys},
 299                 "login_username": {opts.LoginUsername},
 300                 "no_forward":     {fmt.Sprintf("%v", opts.NoForward)},
 301         }
 302         postdata := postform.Encode()
 303         bufw.WriteString("POST " + u.String() + " HTTP/1.1\r\n")
 304         bufw.WriteString("Host: " + u.Host + "\r\n")
 305         bufw.WriteString("Upgrade: ssh\r\n")
 306         bufw.WriteString("X-Arvados-Container-Gateway-Uuid: " + opts.UUID + "\r\n")
 307         bufw.WriteString("X-Arvados-Authorization: " + requestAuth + "\r\n")
 308         bufw.WriteString("Content-Type: application/x-www-form-urlencoded\r\n")
 309         fmt.Fprintf(bufw, "Content-Length: %d\r\n", len(postdata))
 310         bufw.WriteString("\r\n")
 311         bufw.WriteString(postdata)
 312         bufw.Flush()
 313         resp, err := http.ReadResponse(bufr, &http.Request{Method: "POST"})
 314         if err != nil {
 315                 tlsconn.Close()
 316                 return sshconn, httpserver.ErrorWithStatus(fmt.Errorf("error reading http response from gateway: %w", err), http.StatusBadGateway)
 317         }
 318         defer resp.Body.Close()
 319         if resp.StatusCode != http.StatusSwitchingProtocols {
 320                 body, _ := ioutil.ReadAll(io.LimitReader(resp.Body, 1000))
 321                 tlsconn.Close()
 322                 return sshconn, httpserver.ErrorWithStatus(fmt.Errorf("unexpected status %s %q", resp.Status, body), http.StatusBadGateway)
 323         }
 324         if strings.ToLower(resp.Header.Get("Upgrade")) != "ssh" ||
 325                 strings.ToLower(resp.Header.Get("Connection")) != "upgrade" {
 326                 tlsconn.Close()
 327                 return sshconn, httpserver.ErrorWithStatus(errors.New("bad upgrade"), http.StatusBadGateway)
 328         }
 329         if resp.Header.Get("X-Arvados-Authorization-Response") != respondAuth {
 330                 tlsconn.Close()
 331                 return sshconn, httpserver.ErrorWithStatus(errors.New("bad X-Arvados-Authorization-Response header"), http.StatusBadGateway)
 332         }
 333
 334         if !ctr.InteractiveSessionStarted {
 335                 _, err = conn.railsProxy.ContainerUpdate(ctxRoot, arvados.UpdateOptions{
 336                         UUID: opts.UUID,
 337                         Attrs: map[string]interface{}{
 338                                 "interactive_session_started": true,
 339                         },
 340                 })
 341                 if err != nil {
 342                         tlsconn.Close()
 343                         return sshconn, httpserver.ErrorWithStatus(err, http.StatusInternalServerError)
 344                 }
 345         }
 346
 347         sshconn.Conn = tlsconn
 348         sshconn.Bufrw = &bufio.ReadWriter{Reader: bufr, Writer: bufw}
 349         sshconn.Logger = ctxlog.FromContext(ctx)
 350         sshconn.Header = http.Header{"Upgrade": {"ssh"}}
 351         return sshconn, nil
 352 }
 353
 354 // ContainerGatewayTunnel sets up a tunnel enabling us (controller) to
 355 // connect to the caller's (crunch-run's) gateway server.
 356 func (conn *Conn) ContainerGatewayTunnel(ctx context.Context, opts arvados.ContainerGatewayTunnelOptions) (resp arvados.ConnectionResponse, err error) {
 357         h := hmac.New(sha256.New, []byte(conn.cluster.SystemRootToken))
 358         fmt.Fprint(h, opts.UUID)
 359         authSecret := fmt.Sprintf("%x", h.Sum(nil))
 360         if subtle.ConstantTimeCompare([]byte(authSecret), []byte(opts.AuthSecret)) != 1 {
 361                 ctxlog.FromContext(ctx).Info("received incorrect auth_secret")
 362                 return resp, httpserver.ErrorWithStatus(errors.New("authentication error"), http.StatusUnauthorized)
 363         }
 364
 365         muxconn, clientconn := net.Pipe()
 366         tunnel, err := yamux.Server(muxconn, nil)
 367         if err != nil {
 368                 clientconn.Close()
 369                 return resp, httpserver.ErrorWithStatus(err, http.StatusInternalServerError)
 370         }
 371
 372         conn.gwTunnelsLock.Lock()
 373         if conn.gwTunnels == nil {
 374                 conn.gwTunnels = map[string]*yamux.Session{opts.UUID: tunnel}
 375         } else {
 376                 conn.gwTunnels[opts.UUID] = tunnel
 377         }
 378         conn.gwTunnelsLock.Unlock()
 379
 380         go func() {
 381                 <-tunnel.CloseChan()
 382                 conn.gwTunnelsLock.Lock()
 383                 if conn.gwTunnels[opts.UUID] == tunnel {
 384                         delete(conn.gwTunnels, opts.UUID)
 385                 }
 386                 conn.gwTunnelsLock.Unlock()
 387         }()
 388
 389         // Assuming we're acting as the backend of an http server,
 390         // lib/controller/router will call resp's ServeHTTP handler,
 391         // which upgrades the incoming http connection to a raw socket
 392         // and connects it to our yamux.Server through our net.Pipe().
 393         resp.Conn = clientconn
 394         resp.Bufrw = &bufio.ReadWriter{Reader: bufio.NewReader(&bytes.Buffer{}), Writer: bufio.NewWriter(&bytes.Buffer{})}
 395         resp.Logger = ctxlog.FromContext(ctx)
 396         resp.Header = http.Header{"Upgrade": {"tunnel"}}
 397         if u, ok := service.URLFromContext(ctx); ok {
 398                 resp.Header.Set("X-Arvados-Internal-Url", u.String())
 399         } else if forceInternalURLForTest != nil {
 400                 resp.Header.Set("X-Arvados-Internal-Url", forceInternalURLForTest.String())
 401         }
 402         return
 403 }
 404
 405 type gatewayDialer func() (conn net.Conn, requestAuth, respondAuth string, err error)
 406
 407 // findGateway figures out how to connect to ctr's gateway.
 408 //
 409 // If the gateway can be contacted directly or through a tunnel on
 410 // this instance, the first return value is a non-nil dialer.
 411 //
 412 // If the gateway is only accessible through a tunnel through a
 413 // different controller process, the second return value is a non-nil
 414 // *rpc.Conn for that controller.
 415 func (conn *Conn) findGateway(ctx context.Context, ctr arvados.Container, noForward bool) (gatewayDialer, *rpc.Conn, error) {
 416         conn.gwTunnelsLock.Lock()
 417         tunnel := conn.gwTunnels[ctr.UUID]
 418         conn.gwTunnelsLock.Unlock()
 419
 420         myURL, _ := service.URLFromContext(ctx)
 421
 422         if host, _, splitErr := net.SplitHostPort(ctr.GatewayAddress); splitErr == nil && host != "" && host != "127.0.0.1" {
 423                 // If crunch-run provided a GatewayAddress like
 424                 // "ipaddr:port", that means "ipaddr" is one of the
 425                 // external interfaces where the gateway is
 426                 // listening. In that case, it's the most
 427                 // reliable/direct option, so we use it even if a
 428                 // tunnel might also be available.
 429                 return func() (net.Conn, string, string, error) {
 430                         rawconn, err := (&net.Dialer{}).DialContext(ctx, "tcp", ctr.GatewayAddress)
 431                         if err != nil {
 432                                 err = httpserver.ErrorWithStatus(err, http.StatusServiceUnavailable)
 433                         }
 434                         return conn.dialGatewayTLS(ctx, ctr, rawconn)
 435                 }, nil, nil
 436         }
 437         if tunnel != nil && !(forceProxyForTest && !noForward) {
 438                 // If we can't connect directly, and the gateway has
 439                 // established a yamux tunnel with us, connect through
 440                 // the tunnel.
 441                 //
 442                 // ...except: forceProxyForTest means we are emulating
 443                 // a situation where the gateway has established a
 444                 // yamux tunnel with controller B, and the
 445                 // ContainerSSH request arrives at controller A. If
 446                 // noForward==false then we are acting as A, so
 447                 // we pretend not to have a tunnel, and fall through
 448                 // to the "tunurl" case below. If noForward==true
 449                 // then the client is A and we are acting as B, so we
 450                 // connect to our tunnel.
 451                 return func() (net.Conn, string, string, error) {
 452                         rawconn, err := tunnel.Open()
 453                         if err != nil {
 454                                 err = httpserver.ErrorWithStatus(err, http.StatusServiceUnavailable)
 455                         }
 456                         return conn.dialGatewayTLS(ctx, ctr, rawconn)
 457                 }, nil, nil
 458         }
 459         if tunurl := strings.TrimPrefix(ctr.GatewayAddress, "tunnel "); tunurl != ctr.GatewayAddress &&
 460                 tunurl != "" &&
 461                 tunurl != myURL.String() &&
 462                 !noForward {
 463                 // If crunch-run provided a GatewayAddress like
 464                 // "tunnel https://10.0.0.10:1010/", that means the
 465                 // gateway has established a yamux tunnel with the
 466                 // controller process at the indicated InternalURL
 467                 // (which isn't us, otherwise we would have had
 468                 // "tunnel != nil" above). We need to proxy through to
 469                 // the other controller process in order to use the
 470                 // tunnel.
 471                 for u := range conn.cluster.Services.Controller.InternalURLs {
 472                         if u.String() == tunurl {
 473                                 ctxlog.FromContext(ctx).Debugf("connecting to container gateway through other controller at %s", u)
 474                                 u := url.URL(u)
 475                                 return nil, rpc.NewConn(conn.cluster.ClusterID, &u, conn.cluster.TLS.Insecure, rpc.PassthroughTokenProvider), nil
 476                         }
 477                 }
 478                 ctxlog.FromContext(ctx).Warnf("container gateway provided a tunnel endpoint %s that is not one of Services.Controller.InternalURLs", tunurl)
 479                 return nil, nil, httpserver.ErrorWithStatus(errors.New("container gateway is running but tunnel endpoint is invalid"), http.StatusServiceUnavailable)
 480         }
 481         if ctr.GatewayAddress == "" {
 482                 return nil, nil, httpserver.ErrorWithStatus(errors.New("container is running but gateway is not available"), http.StatusServiceUnavailable)
 483         } else {
 484                 return nil, nil, httpserver.ErrorWithStatus(errors.New("container is running but tunnel is down"), http.StatusServiceUnavailable)
 485         }
 486 }
 487
 488 // dialGatewayTLS negotiates a TLS connection to a container gateway
 489 // over the given raw connection.
 490 func (conn *Conn) dialGatewayTLS(ctx context.Context, ctr arvados.Container, rawconn net.Conn) (*tls.Conn, string, string, error) {
 491         // crunch-run uses a self-signed / unverifiable TLS
 492         // certificate, so we use the following scheme to ensure we're
 493         // not talking to an attacker-in-the-middle.
 494         //
 495         // 1. Compute ctrKey = HMAC-SHA256(sysRootToken,ctrUUID) --
 496         // this will be the same ctrKey that a-d-c supplied to
 497         // crunch-run in the GatewayAuthSecret env var.
 498         //
 499         // 2. Compute requestAuth = HMAC-SHA256(ctrKey,serverCert) and
 500         // send it to crunch-run as the X-Arvados-Authorization
 501         // header, proving that we know ctrKey. (Note a MITM cannot
 502         // replay the proof to a real crunch-run server, because the
 503         // real crunch-run server would have a different cert.)
 504         //
 505         // 3. Compute respondAuth = HMAC-SHA256(ctrKey,requestAuth)
 506         // and ensure the server returns it in the
 507         // X-Arvados-Authorization-Response header, proving that the
 508         // server knows ctrKey.
 509         var requestAuth, respondAuth string
 510         tlsconn := tls.Client(rawconn, &tls.Config{
 511                 InsecureSkipVerify: true,
 512                 VerifyPeerCertificate: func(rawCerts [][]byte, verifiedChains [][]*x509.Certificate) error {
 513                         if len(rawCerts) == 0 {
 514                                 return errors.New("no certificate received, cannot compute authorization header")
 515                         }
 516                         h := hmac.New(sha256.New, []byte(conn.cluster.SystemRootToken))
 517                         fmt.Fprint(h, ctr.UUID)
 518                         authKey := fmt.Sprintf("%x", h.Sum(nil))
 519                         h = hmac.New(sha256.New, []byte(authKey))
 520                         h.Write(rawCerts[0])
 521                         requestAuth = fmt.Sprintf("%x", h.Sum(nil))
 522                         h.Reset()
 523                         h.Write([]byte(requestAuth))
 524                         respondAuth = fmt.Sprintf("%x", h.Sum(nil))
 525                         return nil
 526                 },
 527         })
 528         err := tlsconn.HandshakeContext(ctx)
 529         if err != nil {
 530                 return nil, "", "", httpserver.ErrorWithStatus(fmt.Errorf("TLS handshake failed: %w", err), http.StatusBadGateway)
 531         }
 532         if respondAuth == "" {
 533                 tlsconn.Close()
 534                 return nil, "", "", httpserver.ErrorWithStatus(errors.New("BUG: no respondAuth"), http.StatusInternalServerError)
 535         }
 536         return tlsconn, requestAuth, respondAuth, nil
 537 }