KTOR-1464 Fix client Digest auth realm handling

ktor-client/ktor-client-features/ktor-client-auth/common/src/io/ktor/client/features/auth/Auth.kt

@@ -50,6 +50,7 @@ public class Auth(
 
                     val request = HttpRequestBuilder()
                     request.takeFromWithExecutionContext(context)
+                    request.attributes.put(AuthHeaderAttribute, authHeader)
                     provider.addRequestHeaders(request)
                     request.attributes.put(circuitBreaker, Unit)
 
@@ -67,3 +68,11 @@ public class Auth(
 public fun HttpClientConfig<*>.Auth(block: Auth.() -> Unit) {
     install(Auth, block)
 }
+
+/**
+ * AuthHeader from the previous unsuccessful request. This actually should be passed as
+ * parameter to AuthProvider.addRequestHeaders instead in the future and the attribute will
+ * be removed after that.
+ */
+@PublicAPICandidate("1.6.0")
+internal val AuthHeaderAttribute = AttributeKey<HttpAuthHeader>("AuthHeader")

ktor-client/ktor-client-features/ktor-client-auth/common/src/io/ktor/client/features/auth/providers/DigestAuthProvider.kt

@@ -55,14 +55,18 @@ public class DigestAuthProvider(
 
     override fun isApplicable(auth: HttpAuthHeader): Boolean {
         if (auth !is HttpAuthHeader.Parameterized ||
-            auth.parameter("realm") != realm ||
             auth.authScheme != AuthScheme.Digest
         ) return false
 
         val newNonce = auth.parameter("nonce") ?: return false
         val newQop = auth.parameter("qop")
         val newOpaque = auth.parameter("opaque")
 
+        val newRealm = auth.parameter("realm") ?: return false
+        if (newRealm != realm && realm != null) {
+            return false
+        }
+
         serverNonce.value = newNonce
         qop.value = newQop
         opaque.value = newOpaque
@@ -90,6 +94,9 @@ public class DigestAuthProvider(
         }
 
         val token = makeDigest(tokenSequence.joinToString(":"))
+        val realm = realm ?: request.attributes.getOrNull(AuthHeaderAttribute)?.let { auth ->
+            (auth as? HttpAuthHeader.Parameterized)?.parameter("realm")
+        }
 
         val auth = HttpAuthHeader.Parameterized(
             AuthScheme.Digest,

ktor-client/ktor-client-features/ktor-client-auth/common/test/io/ktor/client/features/auth/DigestProviderTest.kt

@@ -56,6 +56,32 @@ class DigestProviderTest {
         checkStandardFields(authHeader)
     }
 
+    @Test
+    fun addRequestHeadersMissingRealm() = testSuspend {
+        if (!PlatformUtils.IS_JVM) return@testSuspend
+
+        val providerWithoutRealm = DigestAuthProvider("username", "pass", null)
+        val authHeader = parseAuthorizationHeader(authAllFields)!!
+        requestBuilder.attributes.put(AuthHeaderAttribute, authHeader)
+
+        assertTrue(providerWithoutRealm.isApplicable(authHeader))
+        providerWithoutRealm.addRequestHeaders(requestBuilder)
+
+        val resultAuthHeader = requestBuilder.headers[HttpHeaders.Authorization]!!
+        checkStandardFields(resultAuthHeader)
+    }
+
+    @Test
+    fun addRequestHeadersChangedRealm() = testSuspend {
+        if (!PlatformUtils.IS_JVM) return@testSuspend
+
+        val providerWithoutRealm = DigestAuthProvider("username", "pass", "wrong!")
+        val authHeader = parseAuthorizationHeader(authAllFields)!!
+        requestBuilder.attributes.put(AuthHeaderAttribute, authHeader)
+
+        assertFalse(providerWithoutRealm.isApplicable(authHeader))
+    }
+
     @Test
     fun addRequestHeadersOmitsQopAndOpaqueWhenMissing() = testSuspend {
         if (!PlatformUtils.IS_JVM) return@testSuspend