feat: ability to parse JWT encoded profile claims (#3014)

* fix: parse JWT profile claims

* Comment with OIDC specs reference

* fix: formatting

* Updated changelog

---------

Co-authored-by: Jan Larwig <jan@larwig.com>

CHANGELOG.md

@@ -12,6 +12,7 @@
 - [#3001](https://github.com/oauth2-proxy/oauth2-proxy/pull/3001) Allow to set non-default authorization request response mode (@stieler-it)
 - [#3041](https://github.com/oauth2-proxy/oauth2-proxy/pull/3041) chore(deps): upgrade to latest golang v1.23.x release (@TheImplementer)
 - [#1916](https://github.com/oauth2-proxy/oauth2-proxy/pull/1916) fix: role extraction from access token in keycloak oidc (@Elektordi / @tuunit)
+- [#3014](https://github.com/oauth2-proxy/oauth2-proxy/pull/3014) feat: ability to parse JWT encoded profile claims (@ikarius)
 
 # V7.8.2
 

pkg/providers/util/claim_extractor.go

@@ -5,6 +5,7 @@ import (
 	"encoding/base64"
 	"encoding/json"
 	"fmt"
+	"mime"
 	"net/http"
 	"net/url"
 	"strings"
@@ -94,11 +95,25 @@ func (c *claimExtractor) loadProfileClaims() (*simplejson.Json, error) {
 		return simplejson.New(), nil
 	}
 
-	claims, err := requests.New(c.profileURL.String()).
+	builder := requests.New(c.profileURL.String()).
 		WithContext(c.ctx).
 		WithHeaders(c.requestHeaders).
-		Do().
-		UnmarshalSimpleJSON()
+		Do()
+
+	// We first check if the result is a JWT token
+	// https://openid.net/specs/openid-connect-core-1_0-final.html#UserInfoResponse
+	mediaType, _, parseErr := mime.ParseMediaType(builder.Headers().Get("Content-Type"))
+
+	if parseErr == nil && mediaType == "application/jwt" {
+		// Decode and use JWT payload as profile claims
+		if pl, err := parseJWT(string(builder.Body())); err == nil {
+			return simplejson.NewJson(pl)
+		}
+	}
+
+	// Otherwise, process as normal JSON payload
+	claims, err := builder.UnmarshalSimpleJSON()
+
 	if err != nil {
 		return nil, fmt.Errorf("error making request to profile URL: %v", err)
 	}

pkg/providers/util/claim_extractor_test.go

@@ -497,6 +497,54 @@ var _ = Describe("Claim Extractor Suite", func() {
 			expectedDst: stringPointer("{\"foo\":[\"bar\",\"baz\"]}"),
 		}),
 	)
+
+	It("should extract claims from a JWT response", func() {
+		jwtResponsePayload := `{
+			"user": "jwtUser",
+			"email": "jwtEmail",
+			"groups": [
+				"jwtGroup1",
+				"jwtGroup2"
+			]
+		}`
+
+		jwtResponseHandler := func(rw http.ResponseWriter, req *http.Request) {
+			if !hasAuthorizedHeader(req.Header) {
+				rw.WriteHeader(403)
+				rw.Write([]byte("Unauthorized"))
+				return
+			}
+
+			rw.Header().Set("Content-Type", "application/jwt; charset=utf-8")
+			rw.Write([]byte(createJWTFromPayload(jwtResponsePayload)))
+		}
+
+		claimExtractor, serverClose, err := newTestClaimExtractor(testClaimExtractorOpts{
+			idTokenPayload:        emptyJSON,
+			setProfileURL:         true,
+			profileRequestHeaders: newAuthorizedHeader(),
+			profileRequestHandler: jwtResponseHandler,
+		})
+		Expect(err).ToNot(HaveOccurred())
+		if serverClose != nil {
+			defer serverClose()
+		}
+
+		value, exists, err := claimExtractor.GetClaim("user")
+		Expect(err).ToNot(HaveOccurred())
+		Expect(exists).To(BeTrue())
+		Expect(value).To(Equal("jwtUser"))
+
+		value, exists, err = claimExtractor.GetClaim("email")
+		Expect(err).ToNot(HaveOccurred())
+		Expect(exists).To(BeTrue())
+		Expect(value).To(Equal("jwtEmail"))
+
+		value, exists, err = claimExtractor.GetClaim("groups")
+		Expect(err).ToNot(HaveOccurred())
+		Expect(exists).To(BeTrue())
+		Expect(value).To(Equal([]interface{}{"jwtGroup1", "jwtGroup2"}))
+	})
 })
 
 // ******************************************