OAuth2: Handle DEFLATE compressed JWT payloads for generic OAuth (#26969)

pkg/login/social/generic_oauth.go

 package social
 
 import (
+	"bytes"
+	"compress/zlib"
 	"encoding/base64"
 	"encoding/json"
 	"errors"
 	"fmt"
+	"io/ioutil"
 	"net/http"
 	"net/mail"
 	"regexp"
 
-	"github.com/grafana/grafana/pkg/util/errutil"
-
 	"github.com/grafana/grafana/pkg/models"
+	"github.com/grafana/grafana/pkg/util/errutil"
 	"golang.org/x/oauth2"
 )
 
@@ -209,6 +211,37 @@ func (s *SocialGenericOAuth) extractFromToken(token *oauth2.Token) *UserInfoJson
 		return nil
 	}
 
+	headerBytes, err := base64.RawURLEncoding.DecodeString(matched[1])
+	if err != nil {
+		s.log.Error("Error base64 decoding header", "header", matched[1], "error", err)
+		return nil
+	}
+
+	var header map[string]string
+	if err := json.Unmarshal(headerBytes, &header); err != nil {
+		s.log.Error("Error deserializing header", "error", err)
+		return nil
+	}
+
+	if compression, ok := header["zip"]; ok {
+		if compression != "DEF" {
+			s.log.Warn("Unknown compression algorithm", "algorithm", compression)
+			return nil
+		}
+
+		fr, err := zlib.NewReader(bytes.NewReader(rawJSON))
+		if err != nil {
+			s.log.Error("Error creating zlib reader", "error", err)
+			return nil
+		}
+		defer fr.Close()
+		rawJSON, err = ioutil.ReadAll(fr)
+		if err != nil {
+			s.log.Error("Error decompressing payload", "error", err)
+			return nil
+		}
+	}
+
 	var data UserInfoJson
 	if err := json.Unmarshal(rawJSON, &data); err != nil {
 		s.log.Error("Error decoding id_token JSON", "raw_json", string(data.rawJSON), "error", err)

pkg/login/social/generic_oauth_test.go

@@ -427,3 +427,64 @@ func TestUserInfoSearchesForLogin(t *testing.T) {
 		}
 	})
 }
+
+func TestPayloadCompression(t *testing.T) {
+	provider := SocialGenericOAuth{
+		SocialBase: &SocialBase{
+			log: log.NewWithLevel("generic_oauth_test", log15.LvlDebug),
+		},
+		emailAttributePath: "email",
+	}
+
+	tests := []struct {
+		Name          string
+		OAuth2Extra   interface{}
+		ExpectedEmail string
+	}{
+		{
+			Name: "Given a valid DEFLATE compressed id_token, return userInfo",
+			OAuth2Extra: map[string]interface{}{
+				// { "role": "Admin", "email": "john.doe@example.com" }
+				"id_token": "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCIsInppcCI6IkRFRiJ9.eJyrVkrNTczMUbJSysrPyNNLyU91SK1IzC3ISdVLzs9V0lEqys9JBco6puRm5inVAgCFRw_6.XrV4ZKhw19dTcnviXanBD8lwjeALCYtDiESMmGzC-ho",
+			},
+			ExpectedEmail: "john.doe@example.com",
+		},
+		{
+			Name: "Given an invalid DEFLATE compressed id_token, return nil",
+			OAuth2Extra: map[string]interface{}{
+				// { "role": "Admin", "email": "john.doe@example.com" }
+				"id_token": "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCIsInppcCI6IkRFRiJ9.00eJyrVkrNTczMUbJSysrPyNNLyU91SK1IzC3ISdVLzs9V0lEqys9JBco6puRm5inVAgCFRw_6.XrV4ZKhw19dTcnviXanBD8lwjeALCYtDiESMmGzC-ho",
+			},
+			ExpectedEmail: "",
+		},
+		{
+			Name: "Given an unsupported GZIP compressed id_token, return nil",
+			OAuth2Extra: map[string]interface{}{
+				// { "role": "Admin", "email": "john.doe@example.com" }
+				"id_token": "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCIsInppcCI6IkdaSVAifQ.H4sIAAAAAAAAAKtWSs1NzMxRslLKys_I00vJT3VIrUjMLchJ1UvOz1XSUSrKz0kFyjqm5GbmKdUCANotxTkvAAAA.85AXm3JOF5qflEA0goDFvlbZl2q3eFvqVcehz860W-o",
+			},
+			ExpectedEmail: "",
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.Name, func(t *testing.T) {
+			staticToken := oauth2.Token{
+				AccessToken:  "",
+				TokenType:    "",
+				RefreshToken: "",
+				Expiry:       time.Now(),
+			}
+
+			token := staticToken.WithExtra(test.OAuth2Extra)
+			userInfo := provider.extractFromToken(token)
+
+			if test.ExpectedEmail == "" {
+				require.Nil(t, userInfo, "Testing case %q", test.Name)
+			} else {
+				require.NotNil(t, userInfo, "Testing case %q", test.Name)
+				require.Equal(t, test.ExpectedEmail, userInfo.Email)
+			}
+		})
+	}
+}