serve: add auth proxy infrastructure

cmd/serve/proxy/proxy.go

@@ -0,0 +1,270 @@
+// Package proxy implements a programmable proxy for rclone serve
+package proxy
+
+import (
+	"bytes"
+	"encoding/json"
+	"os/exec"
+	"strings"
+	"time"
+
+	"github.com/pkg/errors"
+	"github.com/rclone/rclone/fs"
+	"github.com/rclone/rclone/fs/cache"
+	"github.com/rclone/rclone/fs/config/configmap"
+	"github.com/rclone/rclone/fs/config/obscure"
+	libcache "github.com/rclone/rclone/lib/cache"
+	"github.com/rclone/rclone/vfs"
+	"github.com/rclone/rclone/vfs/vfsflags"
+	"golang.org/x/crypto/bcrypt"
+)
+
+// 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.
+
+There is an example program
+[bin/test_proxy.py](https://github.com/rclone/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
+
+For example the program might take this on STDIN
+
+|||
+{
+	"user": "me",
+	"pass": "mypassword"
+}
+|||
+
+And 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| 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|.  This also means that if a user's
+password 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 []byte   // bcrypt hash of the password
+}
+
+// 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, pass string, passwordBytes []byte) (value interface{}, err error) {
+	// Contact the proxy
+	config, err := p.run(map[string]string{
+		"user": user,
+		"pass": pass,
+	})
+	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
+		}
+		pwHash, err := bcrypt.GenerateFromPassword(passwordBytes, bcrypt.DefaultCost)
+		if err != nil {
+			return nil, false, err
+		}
+		entry := cacheEntry{
+			vfs:    vfs.New(f, &vfsflags.Opt),
+			pwHash: pwHash,
+		}
+		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 given input, returning a *vfs.VFS
+// and the key used in the VFS cache.
+func (p *Proxy) Call(user, pass string) (VFS *vfs.VFS, vfsKey string, err error) {
+	var passwordBytes = []byte(pass)
+
+	// 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, pass, passwordBytes)
+		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 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.
+	err = bcrypt.CompareHashAndPassword(entry.pwHash, passwordBytes)
+	if err != nil {
+		return nil, "", errors.Wrap(err, "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
+}