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proxy.go
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proxy.go
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// Package proxy implements a programmable proxy for rclone serve
package proxy
import (
"bytes"
"crypto/sha256"
"crypto/subtle"
"encoding/json"
"os/exec"
"strings"
"time"
"github.com/pkg/errors"
"github.com/artpar/rclone/fs"
"github.com/artpar/rclone/fs/cache"
"github.com/artpar/rclone/fs/config/configmap"
"github.com/artpar/rclone/fs/config/obscure"
libcache "github.com/artpar/rclone/lib/cache"
"github.com/artpar/rclone/vfs"
"github.com/artpar/rclone/vfs/vfsflags"
)
// Help contains text describing how to use the proxy
var Help = strings.Replace(`
### Auth Proxy
If you supply the parameter |--auth-proxy /path/to/program| then
rclone will use that program to generate backends on the fly which
then are used to authenticate incoming requests. This uses a simple
JSON based protocl with input on STDIN and output on STDOUT.
**PLEASE NOTE:** |--auth-proxy| and |--authorized-keys| cannot be used
together, if |--auth-proxy| is set the authorized keys option will be
ignored.
There is an example program
[bin/test_proxy.py](https://github.com/artpar/rclone/blob/master/test_proxy.py)
in the rclone source code.
The program's job is to take a |user| and |pass| on the input and turn
those into the config for a backend on STDOUT in JSON format. This
config will have any default parameters for the backend added, but it
won't use configuration from environment variables or command line
options - it is the job of the proxy program to make a complete
config.
This config generated must have this extra parameter
- |_root| - root to use for the backend
And it may have this parameter
- |_obscure| - comma separated strings for parameters to obscure
If password authentication was used by the client, input to the proxy
process (on STDIN) would look similar to this:
|||
{
"user": "me",
"pass": "mypassword"
}
|||
If public-key authentication was used by the client, input to the
proxy process (on STDIN) would look similar to this:
|||
{
"user": "me",
"public_key": "AAAAB3NzaC1yc2EAAAADAQABAAABAQDuwESFdAe14hVS6omeyX7edc...JQdf"
}
|||
And as an example return this on STDOUT
|||
{
"type": "sftp",
"_root": "",
"_obscure": "pass",
"user": "me",
"pass": "mypassword",
"host": "sftp.example.com"
}
|||
This would mean that an SFTP backend would be created on the fly for
the |user| and |pass|/|public_key| returned in the output to the host given. Note
that since |_obscure| is set to |pass|, rclone will obscure the |pass|
parameter before creating the backend (which is required for sftp
backends).
The progam can manipulate the supplied |user| in any way, for example
to make proxy to many different sftp backends, you could make the
|user| be |user@example.com| and then set the |host| to |example.com|
in the output and the user to |user|. For security you'd probably want
to restrict the |host| to a limited list.
Note that an internal cache is keyed on |user| so only use that for
configuration, don't use |pass| or |public_key|. This also means that if a user's
password or public-key is changed the cache will need to expire (which takes 5 mins)
before it takes effect.
This can be used to build general purpose proxies to any kind of
backend that rclone supports.
`, "|", "`", -1)
// Options is options for creating the proxy
type Options struct {
AuthProxy string
}
// DefaultOpt is the default values uses for Opt
var DefaultOpt = Options{
AuthProxy: "",
}
// Proxy represents a proxy to turn auth requests into a VFS
type Proxy struct {
cmdLine []string // broken down command line
vfsCache *libcache.Cache
Opt Options
}
// cacheEntry is what is stored in the vfsCache
type cacheEntry struct {
vfs *vfs.VFS // stored VFS
pwHash [sha256.Size]byte // sha256 hash of the password/publicKey
}
// New creates a new proxy with the Options passed in
func New(opt *Options) *Proxy {
return &Proxy{
Opt: *opt,
cmdLine: strings.Fields(opt.AuthProxy),
vfsCache: libcache.New(),
}
}
// run the proxy command returning a config map
func (p *Proxy) run(in map[string]string) (config configmap.Simple, err error) {
cmd := exec.Command(p.cmdLine[0], p.cmdLine[1:]...)
inBytes, err := json.MarshalIndent(in, "", "\t")
if err != nil {
return nil, errors.Wrap(err, "Proxy.Call failed to marshal input: %v")
}
var stdout, stderr bytes.Buffer
cmd.Stdin = bytes.NewBuffer(inBytes)
cmd.Stdout = &stdout
cmd.Stderr = &stderr
start := time.Now()
err = cmd.Run()
fs.Debugf(nil, "Calling proxy %v", p.cmdLine)
duration := time.Since(start)
if err != nil {
return nil, errors.Wrapf(err, "proxy: failed on %v: %q", p.cmdLine, strings.TrimSpace(string(stderr.Bytes())))
}
err = json.Unmarshal(stdout.Bytes(), &config)
if err != nil {
return nil, errors.Wrapf(err, "proxy: failed to read output: %q", string(stdout.Bytes()))
}
fs.Debugf(nil, "Proxy returned in %v", duration)
// Obscure any values in the config map that need it
obscureFields, ok := config.Get("_obscure")
if ok {
for _, key := range strings.Split(obscureFields, ",") {
value, ok := config.Get(key)
if ok {
obscuredValue, err := obscure.Obscure(value)
if err != nil {
return nil, errors.Wrap(err, "proxy")
}
config.Set(key, obscuredValue)
}
}
}
return config, nil
}
// call runs the auth proxy and returns a cacheEntry and an error
func (p *Proxy) call(user, auth string, isPublicKey bool) (value interface{}, err error) {
var config configmap.Simple
// Contact the proxy
if isPublicKey {
config, err = p.run(map[string]string{
"user": user,
"public_key": auth,
})
} else {
config, err = p.run(map[string]string{
"user": user,
"pass": auth,
})
}
if err != nil {
return nil, err
}
// Look for required fields in the answer
fsName, ok := config.Get("type")
if !ok {
return nil, errors.New("proxy: type not set in result")
}
root, ok := config.Get("_root")
if !ok {
return nil, errors.New("proxy: _root not set in result")
}
// Find the backend
fsInfo, err := fs.Find(fsName)
if err != nil {
return nil, errors.Wrapf(err, "proxy: couldn't find backend for %q", fsName)
}
// base name of config on user name. This may appear in logs
name := "proxy-" + user
fsString := name + ":" + root
// Look for fs in the VFS cache
value, err = p.vfsCache.Get(user, func(key string) (value interface{}, ok bool, err error) {
// Create the Fs from the cache
f, err := cache.GetFn(fsString, func(fsString string) (fs.Fs, error) {
// Update the config with the default values
for i := range fsInfo.Options {
o := &fsInfo.Options[i]
if _, found := config.Get(o.Name); !found && o.Default != nil && o.String() != "" {
config.Set(o.Name, o.String())
}
}
return fsInfo.NewFs(name, root, config)
})
if err != nil {
return nil, false, err
}
// We hash the auth here so we don't copy the auth more than we
// need to in memory. An attacker would find it easier to go
// after the unencrypted password in memory most likely.
entry := cacheEntry{
vfs: vfs.New(f, &vfsflags.Opt),
pwHash: sha256.Sum256([]byte(auth)),
}
return entry, true, nil
})
if err != nil {
return nil, errors.Wrapf(err, "proxy: failed to create backend")
}
return value, nil
}
// Call runs the auth proxy with the username and password/public key provided
// returning a *vfs.VFS and the key used in the VFS cache.
func (p *Proxy) Call(user, auth string, isPublicKey bool) (VFS *vfs.VFS, vfsKey string, err error) {
// Look in the cache first
value, ok := p.vfsCache.GetMaybe(user)
// If not found then call the proxy for a fresh answer
if !ok {
value, err = p.call(user, auth, isPublicKey)
if err != nil {
return nil, "", err
}
}
// check we got what we were expecting
entry, ok := value.(cacheEntry)
if !ok {
return nil, "", errors.Errorf("proxy: value is not cache entry: %#v", value)
}
// Check the password / public key is correct in the cached entry. This
// prevents an attack where subsequent requests for the same
// user don't have their auth checked. It does mean that if
// the password is changed, the user will have to wait for
// cache expiry (5m) before trying again.
authHash := sha256.Sum256([]byte(auth))
if subtle.ConstantTimeCompare(authHash[:], entry.pwHash[:]) != 1 {
if isPublicKey {
return nil, "", errors.New("proxy: incorrect public key")
}
return nil, "", errors.New("proxy: incorrect password")
}
return entry.vfs, user, nil
}
// Get VFS from the cache using key - returns nil if not found
func (p *Proxy) Get(key string) *vfs.VFS {
value, ok := p.vfsCache.GetMaybe(key)
if !ok {
return nil
}
entry := value.(cacheEntry)
return entry.vfs
}