Fixes #7758: Fixed JWT token for Jitsi openidtoken-jwt authentication

Signed-off-by: Alexey Nechaev <seysane@yahoo.com>

changelog.d/7758.bugfix

@@ -0,0 +1 @@
+Fixed JWT token for Jitsi openidtoken-jwt authentication

vector/build.gradle

@@ -282,6 +282,7 @@ dependencies {
     runtimeOnly(libs.jsonwebtoken.jjwtOrgjson) {
         exclude group: 'org.json', module: 'json' //provided by Android natively
     }
+    testImplementation(libs.jsonwebtoken.jjwtOrgjson)
     implementation 'commons-codec:commons-codec:1.15'
 
     // MapTiler

vector/src/main/java/im/vector/app/features/call/conference/jwt/JitsiJWTFactory.kt

@@ -19,8 +19,11 @@ package im.vector.app.features.call.conference.jwt
 import im.vector.app.core.utils.ensureProtocol
 import io.jsonwebtoken.Jwts
 import io.jsonwebtoken.SignatureAlgorithm
+import io.jsonwebtoken.io.Encoders
 import io.jsonwebtoken.security.Keys
 import org.matrix.android.sdk.api.session.openid.OpenIdToken
+import javax.crypto.Mac
+import javax.crypto.spec.SecretKeySpec
 import javax.inject.Inject
 
 class JitsiJWTFactory @Inject constructor() {
@@ -37,7 +40,12 @@ class JitsiJWTFactory @Inject constructor() {
             userDisplayName: String
     ): String {
         // The secret key here is irrelevant, we're only using the JWT to transport data to Prosody in the Jitsi stack.
-        val key = Keys.secretKeyFor(SignatureAlgorithm.HS256)
+        // In the PR https://github.com/jitsi/luajwtjitsi/pull/3 the function `luajwtjitsi.decode` was removed and
+        // we cannot use random secret keys anymore. But the JWT library `jjwt` doesn't accept the hardcoded key `notused`
+        // from the module `prosody-mod-auth-matrix-user-verification` since it's too short and thus insecure. So, we
+        // create a new token using a random key and then re-sign the token manually with the 'weak' key.
+        val signatureAlgorithm = SignatureAlgorithm.HS256
+        val key = Keys.secretKeyFor(signatureAlgorithm)
         val context = mapOf(
                 "matrix" to mapOf(
                         "token" to openIdToken.accessToken,
@@ -52,7 +60,8 @@ class JitsiJWTFactory @Inject constructor() {
         // As per Jitsi token auth, `iss` needs to be set to something agreed between
         // JWT generating side and Prosody config. Since we have no configuration for
         // the widgets, we can't set one anywhere. Using the Jitsi domain here probably makes sense.
-        return Jwts.builder()
+        val token = Jwts.builder()
+                .setHeaderParam("typ", "JWT")
                 .setIssuer(jitsiServerDomain)
                 .setSubject(jitsiServerDomain)
                 .setAudience(jitsiServerDomain.ensureProtocol())
@@ -61,5 +70,11 @@ class JitsiJWTFactory @Inject constructor() {
                 .claim("context", context)
                 .signWith(key)
                 .compact()
+        // Re-sign token with the hardcoded key
+        val toSign = token.substring(0, token.lastIndexOf('.'))
+        val mac = Mac.getInstance(signatureAlgorithm.jcaName)
+        mac.init(SecretKeySpec("notused".toByteArray(), mac.algorithm))
+        val prosodySignature = Encoders.BASE64URL.encode(mac.doFinal(toSign.toByteArray()))
+        return "$toSign.$prosodySignature"
     }
 }

vector/src/test/java/im/vector/app/features/call/conference/jwt/JitsiJWTFactoryTest.kt

@@ -0,0 +1,156 @@
+/*
+ * Copyright (c) 2023 New Vector Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package im.vector.app.features.call.conference.jwt
+
+import com.squareup.moshi.JsonAdapter
+import com.squareup.moshi.Moshi
+import com.squareup.moshi.Types
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertTrue
+import org.junit.Before
+import org.junit.Test
+import org.matrix.android.sdk.api.session.openid.OpenIdToken
+import java.lang.reflect.ParameterizedType
+import java.util.Base64
+import kotlin.streams.toList
+
+class JitsiJWTFactoryTest {
+    private val base64Decoder = Base64.getUrlDecoder()
+    private val moshi = Moshi.Builder().build()
+    private val stringToString = Types.newParameterizedType(Map::class.java, String::class.java, String::class.java)
+    private val stringToAny = Types.newParameterizedType(Map::class.java, String::class.java, Any::class.java)
+    private lateinit var factory: JitsiJWTFactory
+
+    @Before
+    fun init() {
+        factory = JitsiJWTFactory()
+    }
+
+    @Test
+    fun `token contains 3 encoded parts`() {
+        val token = createToken()
+
+        val parts = token.split(".")
+        assertEquals(3, parts.size)
+        parts.forEach {
+            assertTrue("Non-empty array", base64Decoder.decode(it).isNotEmpty())
+        }
+    }
+
+    @Test
+    fun `token contains unique signature`() {
+        val signatures = listOf("one", "two").stream()
+                .map { createToken(it) }
+                .map { it.split(".")[2] }
+                .map { base64Decoder.decode(it) }
+                .toList()
+
+        assertEquals(2, signatures.size)
+        signatures.forEach {
+            assertEquals(32, it.size)
+        }
+        assertFalse("Unique", signatures[0].contentEquals(signatures[1]))
+    }
+
+    @Test
+    fun `token header contains algorithm`() {
+        val token = createToken()
+
+        assertEquals("HS256", parseTokenHeader(token)["alg"])
+    }
+
+    @Test
+    fun `token header contains type`() {
+        val token = createToken()
+
+        assertEquals("JWT", parseTokenHeader(token)["typ"])
+    }
+
+    @Test
+    fun `token body contains subject`() {
+        val token = createToken()
+
+        assertEquals("jitsi-server-domain", parseTokenBody(token)["sub"])
+    }
+
+    @Test
+    fun `token body contains issuer`() {
+        val token = createToken()
+
+        assertEquals("jitsi-server-domain", parseTokenBody(token)["iss"])
+    }
+
+    @Test
+    fun `token body contains audience`() {
+        val token = createToken()
+
+        assertEquals("https://jitsi-server-domain", parseTokenBody(token)["aud"])
+    }
+
+    @Test
+    fun `token body contains room claim`() {
+        val token = createToken()
+
+        assertEquals("*", parseTokenBody(token)["room"])
+    }
+
+    @Test
+    fun `token body contains matrix data`() {
+        val token = createToken()
+
+        assertEquals(mutableMapOf("room_id" to "room-id", "server_name" to "matrix-server-name", "token" to "matrix-token"), parseMatrixData(token))
+    }
+
+    @Test
+    fun `token body contains user data`() {
+        val token = createToken()
+
+        assertEquals(mutableMapOf("name" to "user-display-name", "avatar" to "user-avatar-url"), parseUserData(token))
+    }
+
+    private fun createToken(): String {
+        return createToken("matrix-token")
+    }
+
+    private fun createToken(accessToken: String): String {
+        val openIdToken = OpenIdToken(accessToken, "matrix-token-type", "matrix-server-name", -1)
+        return factory.create(openIdToken, "jitsi-server-domain", "room-id", "user-avatar-url", "user-display-name")
+    }
+
+    private fun parseTokenHeader(token: String): Map<String, String> {
+        return parseTokenPart(token.split(".")[0], stringToString)
+    }
+
+    private fun parseTokenBody(token: String): Map<String, Any> {
+        return parseTokenPart(token.split(".")[1], stringToAny)
+    }
+
+    private fun parseMatrixData(token: String): Map<*, *> {
+        return (parseTokenBody(token)["context"] as Map<*, *>)["matrix"] as Map<*, *>
+    }
+
+    private fun parseUserData(token: String): Map<*, *> {
+        return (parseTokenBody(token)["context"] as Map<*, *>)["user"] as Map<*, *>
+    }
+
+    private fun <T> parseTokenPart(value: String, type: ParameterizedType): T {
+        val decoded = String(base64Decoder.decode(value))
+        val adapter: JsonAdapter<T> = moshi.adapter(type)
+        return adapter.fromJson(decoded)!!
+    }
+}