jwtutil: functionality to get an access token via JWT authentication

lib/jwtutil/jwtutil.go

@@ -0,0 +1,87 @@
+package jwtutil
+
+import (
+	"bytes"
+	"crypto/rand"
+	"crypto/rsa"
+	"encoding/hex"
+	"encoding/json"
+	"net/http"
+	"time"
+
+	"github.com/pkg/errors"
+	"github.com/rclone/rclone/fs/config/configmap"
+	"github.com/rclone/rclone/lib/oauthutil"
+
+	"golang.org/x/oauth2"
+	"golang.org/x/oauth2/jws"
+)
+
+// RandomHex creates a random string of the given length
+func RandomHex(n int) (string, error) {
+	bytes := make([]byte, n)
+	if _, err := rand.Read(bytes); err != nil {
+		return "", err
+	}
+	return hex.EncodeToString(bytes), nil
+}
+
+// Config configures rclone using JWT
+func Config(id, name string, claims *jws.ClaimSet, header *jws.Header, queryParams map[string]string, privateKey *rsa.PrivateKey, m configmap.Mapper, client *http.Client) (err error) {
+	payload, err := jws.Encode(header, claims, privateKey)
+	if err != nil {
+		return errors.Wrap(err, "jwtutil: failed to encode payload")
+	}
+	req, err := http.NewRequest("POST", claims.Aud, nil)
+	if err != nil {
+		return errors.Wrap(err, "jwtutil: failed to create new request")
+	}
+	q := req.URL.Query()
+	q.Add("grant_type", "urn:ietf:params:oauth:grant-type:jwt-bearer")
+	q.Add("assertion", payload)
+	for key, value := range queryParams {
+		q.Add(key, value)
+	}
+	queryString := q.Encode()
+
+	req, err = http.NewRequest("POST", claims.Aud, bytes.NewBuffer([]byte(queryString)))
+	if err != nil {
+		return errors.Wrap(err, "jwtutil: failed to create new request")
+	}
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+
+	resp, err := client.Do(req)
+	if err != nil {
+		return errors.Wrap(err, "jwtutil: failed making auth request")
+	}
+	if resp.StatusCode != 200 {
+		return errors.Wrap(err, "jwtutil: failed making auth request")
+	}
+	defer func() {
+		deferedErr := resp.Body.Close()
+		if deferedErr != nil {
+			err = errors.Wrap(err, "jwtutil: failed to close resp.Body")
+		}
+	}()
+
+	result := &response{}
+	err = json.NewDecoder(resp.Body).Decode(result)
+	if err != nil || result.AccessToken == "" {
+		return errors.Wrap(err, "jwtutil: failed to get token")
+	}
+	token := &oauth2.Token{
+		AccessToken: result.AccessToken,
+		TokenType:   result.TokenType,
+	}
+	e := result.ExpiresIn
+	if e != 0 {
+		token.Expiry = time.Now().Add(time.Duration(e) * time.Second)
+	}
+	return oauthutil.PutToken(name, m, token, true)
+}
+
+type response struct {
+	AccessToken string `json:"access_token"`
+	TokenType   string `json:"token_type"`
+	ExpiresIn   int    `json:"expires_in"`
+}