Fix response body of /3pid/bind to match spec

- synapse did not check/validate the response as per spec until 0.99.5 it seems
- mxisd was never compliant also

src/main/java/io/kamax/mxisd/crypto/CryptoFactory.java

@@ -21,6 +21,7 @@
 package io.kamax.mxisd.crypto;
 
 import io.kamax.mxisd.config.KeyConfig;
+import io.kamax.mxisd.config.MxisdConfig;
 import io.kamax.mxisd.crypto.ed25519.Ed25519KeyManager;
 import io.kamax.mxisd.crypto.ed25519.Ed25519SignatureManager;
 import io.kamax.mxisd.storage.crypto.FileKeyStore;
@@ -54,8 +55,8 @@ public class CryptoFactory {
         return new Ed25519KeyManager(store);
     }
 
-    public static SignatureManager getSignatureManager(Ed25519KeyManager keyMgr) {
-        return new Ed25519SignatureManager(keyMgr);
+    public static SignatureManager getSignatureManager(MxisdConfig cfg, Ed25519KeyManager keyMgr) {
+        return new Ed25519SignatureManager(cfg, keyMgr);
     }
 
 }

src/main/java/io/kamax/mxisd/crypto/SignatureManager.java

@@ -30,6 +30,18 @@ import java.util.Objects;
 
 public interface SignatureManager {
 
+    /**
+     * Sign the message with the default domain and add the signature to the <code>signatures</code> key.
+     * <p>
+     * If the key does not exist yet, it is created. If the key exist, the produced signature will be merged with any
+     * existing ones.
+     *
+     * @param message The message to sign with the default domain and add the produced signature to
+     * @return The provided message with the new signature
+     * @throws IllegalArgumentException If the <code>signatures</code> key exists and its value is not a JSON object
+     */
+    JsonObject signMessageGson(JsonObject message) throws IllegalArgumentException;
+
     /**
      * Sign the message and add the signature to the <code>signatures</code> key.
      * <p>
@@ -39,7 +51,7 @@ public interface SignatureManager {
      * @param domain  The domain under which the signature should be added
      * @param message The message to sign and add the produced signature to
      * @return The provided message with the new signature
-     * @throws IllegalArgumentException If the <code>signatures</code> value is not a JSON object
+     * @throws IllegalArgumentException If the <code>signatures</code> key exists and its value is not a JSON object
      */
     default JsonObject signMessageGson(String domain, JsonObject message) throws IllegalArgumentException {
         JsonElement signEl = message.remove(EventKey.Signatures.get());

src/main/java/io/kamax/mxisd/crypto/ed25519/Ed25519SignatureManager.java

@@ -23,6 +23,8 @@ package io.kamax.mxisd.crypto.ed25519;
 import com.google.gson.JsonObject;
 import io.kamax.matrix.codec.MxBase64;
 import io.kamax.matrix.json.MatrixJson;
+import io.kamax.mxisd.config.MxisdConfig;
+import io.kamax.mxisd.config.ServerConfig;
 import io.kamax.mxisd.crypto.KeyIdentifier;
 import io.kamax.mxisd.crypto.Signature;
 import io.kamax.mxisd.crypto.SignatureManager;
@@ -35,12 +37,19 @@ import java.security.SignatureException;
 
 public class Ed25519SignatureManager implements SignatureManager {
 
+    private final ServerConfig cfg;
     private final Ed25519KeyManager keyMgr;
 
-    public Ed25519SignatureManager(Ed25519KeyManager keyMgr) {
+    public Ed25519SignatureManager(MxisdConfig cfg, Ed25519KeyManager keyMgr) {
+        this.cfg = cfg.getServer();
         this.keyMgr = keyMgr;
     }
 
+    @Override
+    public JsonObject signMessageGson(JsonObject message) throws IllegalArgumentException {
+        return signMessageGson(cfg.getName(), message);
+    }
+
     @Override
     public JsonObject signMessageGson(String domain, String message) {
         Signature sign = sign(message);