FEATURE: add JWT to HTTP endpoints of Filer and use them in S3 Client

- one JWT for reading and one for writing, analogous to how the JWT
  between Master and Volume Server works
- I did not implement IP `whiteList` parameter on the filer

Additionally, because http_util.DownloadFile now sets the JWT,
the `download` command should now work when `jwt.signing.read` is
configured. By looking at the code, I think this case did not work
before.

## Docs to be adjusted after a release

Page `Amazon-S3-API`:

```
# Authentication with Filer

You can use mTLS for the gRPC connection between S3-API-Proxy and the filer, as
explained in [Security-Configuration](Security-Configuration) -
controlled by the `grpc.*` configuration in `security.toml`.

Starting with version XX, it is also possible to authenticate the HTTP
operations between the S3-API-Proxy and the Filer (especially
uploading new files). This is configured by setting
`filer_jwt.signing.key` and `filer_jwt.signing.read.key` in
`security.toml`.

With both configurations (gRPC and JWT), it is possible to have Filer
and S3 communicate in fully authenticated fashion; so Filer will reject
any unauthenticated communication.
```

Page `Security Overview`:

```
The following items are not covered, yet:

- master server http REST services

Starting with version XX, the Filer HTTP REST services can be secured
with a JWT, by setting `filer_jwt.signing.key` and
`filer_jwt.signing.read.key` in `security.toml`.

...

Before version XX: "weed filer -disableHttp", disable http operations, only gRPC operations are allowed. This works with "weed mount" by FUSE. It does **not work** with the [S3 Gateway](Amazon S3 API), as this does HTTP calls to the Filer.
Starting with version XX: secured by JWT, by setting `filer_jwt.signing.key` and `filer_jwt.signing.read.key` in `security.toml`. **This now works with the [S3 Gateway](Amazon S3 API).**

...

# Securing Filer HTTP with JWT

To enable JWT-based access control for the Filer,

1. generate `security.toml` file by `weed scaffold -config=security`
2. set `filer_jwt.signing.key` to a secret string - and optionally filer_jwt.signing.read.key` as well to a secret string
3. copy the same `security.toml` file to the filers and all S3 proxies.

If `filer_jwt.signing.key` is configured: When sending upload/update/delete HTTP operations to a filer server, the request header `Authorization` should be the JWT string (`Authorization: Bearer [JwtToken]`). The operation is authorized after the filer validates the JWT with `filer_jwt.signing.key`.

If `filer_jwt.signing.read.key` is configured: When sending GET or HEAD requests to a filer server, the request header `Authorization` should be the JWT string (`Authorization: Bearer [JwtToken]`). The operation is authorized after the filer validates the JWT with `filer_jwt.signing.read.key`.

The S3 API Gateway reads the above JWT keys and sends authenticated
HTTP requests to the filer.
```

Page `Security Configuration`:

```
(update scaffold file)

...

[filer_jwt.signing]
key = "blahblahblahblah"

[filer_jwt.signing.read]
key = "blahblahblahblah"
```

Resolves: #158

1 files changed, 69 insertions, 9 deletions

diff --git a/weed/server/filer_server_handlers.go b/weed/server/filer_server_handlers.go
index 118646a04..6f0d0b7ca 100644
--- a/weed/server/filer_server_handlers.go
+++ b/weed/server/filer_server_handlers.go
@@ -1,7 +1,9 @@
 package weed_server
 
 import (
+	"errors"
 	"github.com/chrislusf/seaweedfs/weed/glog"
+	"github.com/chrislusf/seaweedfs/weed/security"
 	"github.com/chrislusf/seaweedfs/weed/util"
 	"net/http"
 	"strings"
@@ -15,6 +17,19 @@ func (fs *FilerServer) filerHandler(w http.ResponseWriter, r *http.Request) {
 
 	start := time.Now()
 
+	if r.Method == "OPTIONS" {
+		stats.FilerRequestCounter.WithLabelValues("options").Inc()
+		OptionsHandler(w, r, false)
+		stats.FilerRequestHistogram.WithLabelValues("options").Observe(time.Since(start).Seconds())
+		return
+	}
+
+	isReadHttpCall := r.Method == "GET" || r.Method == "HEAD"
+	if !fs.maybeCheckJwtAuthorization(r, !isReadHttpCall) {
+		writeJsonError(w, r, http.StatusUnauthorized, errors.New("wrong jwt"))
+		return
+	}
+
 	// proxy to volume servers
 	var fileId string
 	if strings.HasPrefix(r.RequestURI, "/?proxyChunkId=") {
@@ -78,20 +93,31 @@ func (fs *FilerServer) filerHandler(w http.ResponseWriter, r *http.Request) {
 			fs.PostHandler(w, r, contentLength)
 			stats.FilerRequestHistogram.WithLabelValues("post").Observe(time.Since(start).Seconds())
 		}
-	case "OPTIONS":
-		stats.FilerRequestCounter.WithLabelValues("options").Inc()
-		OptionsHandler(w, r, false)
-		stats.FilerRequestHistogram.WithLabelValues("head").Observe(time.Since(start).Seconds())
 	}
 }
 
 func (fs *FilerServer) readonlyFilerHandler(w http.ResponseWriter, r *http.Request) {
+
+	start := time.Now()
+
+	// We handle OPTIONS first because it never should be authenticated
+	if r.Method == "OPTIONS" {
+		stats.FilerRequestCounter.WithLabelValues("options").Inc()
+		OptionsHandler(w, r, true)
+		stats.FilerRequestHistogram.WithLabelValues("options").Observe(time.Since(start).Seconds())
+		return
+	}
+
+	if !fs.maybeCheckJwtAuthorization(r, false) {
+		writeJsonError(w, r, http.StatusUnauthorized, errors.New("wrong jwt"))
+		return
+	}
+
 	w.Header().Set("Server", "SeaweedFS Filer "+util.VERSION)
 	if r.Header.Get("Origin") != "" {
 		w.Header().Set("Access-Control-Allow-Origin", "*")
 		w.Header().Set("Access-Control-Allow-Credentials", "true")
 	}
-	start := time.Now()
 	switch r.Method {
 	case "GET":
 		stats.FilerRequestCounter.WithLabelValues("get").Inc()
@@ -101,10 +127,6 @@ func (fs *FilerServer) readonlyFilerHandler(w http.ResponseWriter, r *http.Reque
 		stats.FilerRequestCounter.WithLabelValues("head").Inc()
 		fs.GetOrHeadHandler(w, r)
 		stats.FilerRequestHistogram.WithLabelValues("head").Observe(time.Since(start).Seconds())
-	case "OPTIONS":
-		stats.FilerRequestCounter.WithLabelValues("options").Inc()
-		OptionsHandler(w, r, true)
-		stats.FilerRequestHistogram.WithLabelValues("head").Observe(time.Since(start).Seconds())
 	}
 }
 
@@ -116,3 +138,41 @@ func OptionsHandler(w http.ResponseWriter, r *http.Request, isReadOnly bool) {
 	}
 	w.Header().Add("Access-Control-Allow-Headers", "*")
 }
+
+// maybeCheckJwtAuthorization returns true if access should be granted, false if it should be denied
+func (fs *FilerServer) maybeCheckJwtAuthorization(r *http.Request, isWrite bool) bool {
+
+	var signingKey security.SigningKey
+
+	if isWrite {
+		if len(fs.filerGuard.SigningKey) == 0 {
+			return true
+		} else {
+			signingKey = fs.filerGuard.SigningKey
+		}
+	} else {
+		if len(fs.filerGuard.ReadSigningKey) == 0 {
+			return true
+		} else {
+			signingKey = fs.filerGuard.ReadSigningKey
+		}
+	}
+
+	tokenStr := security.GetJwt(r)
+	if tokenStr == "" {
+		glog.V(1).Infof("missing jwt from %s", r.RemoteAddr)
+		return false
+	}
+
+	token, err := security.DecodeJwt(signingKey, tokenStr, &security.SeaweedFilerClaims{})
+	if err != nil {
+		glog.V(1).Infof("jwt verification error from %s: %v", r.RemoteAddr, err)
+		return false
+	}
+	if !token.Valid {
+		glog.V(1).Infof("jwt invalid from %s: %v", r.RemoteAddr, tokenStr)
+		return false
+	} else {
+		return true
+	}
+}