Token validation refuses login-typed messages

dotnet/EcencyApi.Tests/TokenTypeTests.cs

@@ -0,0 +1,42 @@
+using System.Text.Json.Nodes;
+using EcencyApi.Handlers;
+using Xunit;
+
+namespace EcencyApi.Tests;
+
+/// <summary>
+/// A HiveSigner-style message typed "login" proves who signed it and nothing
+/// more: HiveSigner answers /api/me for one and refuses it everywhere else, and
+/// the Ecency clients never send one (wallet logins send "code", HiveSigner
+/// issues "posting" for the scopes they request). Token validation refuses it
+/// before any key lookup, and leaves every other shape to the signature checks.
+/// </summary>
+public class TokenTypeTests
+{
+    private static JsonNode? Parse(string json) => JsonNode.Parse(json);
+
+    [Fact]
+    public void LoginTypedMessageIsRefused()
+    {
+        Assert.True(PrivateApi.IsLoginOnlyMessage(Parse("""{"type":"login","app":"ecency.app"}""")));
+        Assert.True(PrivateApi.IsLoginOnlyMessage(
+            Parse("""{"type":"login","app":"ecency.app","audience":"honeyback://hive"}""")));
+    }
+
+    [Theory]
+    [InlineData("""{"type":"code","app":"ecency.app"}""")]
+    [InlineData("""{"type":"posting","app":"ecency.app"}""")]
+    [InlineData("""{"type":"offline","app":"ecency.app"}""")]
+    [InlineData("""{"type":"refresh","app":"ecency.app"}""")]
+    [InlineData("""{"type":"Login","app":"ecency.app"}""")]
+    [InlineData("""{"app":"ecency.app"}""")]
+    [InlineData("""{"type":null}""")]
+    [InlineData("""{"type":1}""")]
+    [InlineData("""{"type":["login"]}""")]
+    [InlineData("""["login"]""")]
+    [InlineData("null")]
+    public void EverythingElseIsLeftToTheSignatureChecks(string signedMessage)
+    {
+        Assert.False(PrivateApi.IsLoginOnlyMessage(Parse(signedMessage)));
+    }
+}

dotnet/EcencyApi/Handlers/PrivateApi.Core.cs

@@ -120,6 +120,15 @@ timestampNode is JsonValue timestampValue
                 return null;
             }
 
+            // A message typed "login" only says who signed it. HiveSigner answers
+            // /api/me for one and refuses everything else, and no Ecency client
+            // ever sends one here, so it is not a session here either. Decided
+            // before any node lookup: the shape alone settles it.
+            if (IsLoginOnlyMessage(signedMessage))
+            {
+                return null;
+            }
+
             var currentTime = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds();
 
             // rawMessage = JSON.stringify({ signed_message, authors, timestamp })
@@ -192,6 +201,18 @@ timestampNode is JsonValue timestampValue
         }
     }
 
+    /// <summary>
+    /// True for a signed_message whose type is the string "login": a proof of
+    /// identity for another app, never a session. Anything else, including a
+    /// missing or non-string type, is left to the signature checks as before.
+    /// </summary>
+    internal static bool IsLoginOnlyMessage(JsonNode? signedMessage) =>
+        signedMessage is JsonObject obj
+        && obj.TryGetPropertyValue("type", out var typeNode)
+        && typeNode is JsonValue typeValue
+        && JsVal.TryGetStringLenient(typeValue, out var type)
+        && type == "login";
+
     /// <summary>key_auths.map(([key]) => key) — throws on non-array input like .map on a non-array.</summary>
     private static List<string?> MapKeyAuths(JsonNode? keyAuths)
     {