Add an option to enable/disable hash lookup via the LDAP provider.

src/main/java/io/kamax/mxisd/backend/ldap/LdapThreePidProvider.java

@@ -159,6 +159,10 @@ public class LdapThreePidProvider extends LdapBackend implements IThreePidProvid
     @Override
     public Iterable<ThreePidMapping> populateHashes() {
         List<ThreePidMapping> result = new ArrayList<>();
+        if (!getCfg().getIdentity().isLookup()) {
+            return result;
+        }
+
         String filter = getCfg().getIdentity().getFilter();
 
         try (LdapConnection conn = getConn()) {

src/main/java/io/kamax/mxisd/config/ldap/LdapConfig.java

@@ -233,6 +233,7 @@ public abstract class LdapConfig {
         private String filter;
         private String token = "%3pid";
         private Map<String, String> medium = new HashMap<>();
+        private boolean lookup = false;
 
         public String getFilter() {
             return filter;
@@ -262,6 +263,13 @@ public abstract class LdapConfig {
             this.medium = medium;
         }
 
+        public boolean isLookup() {
+            return lookup;
+        }
+
+        public void setLookup(boolean lookup) {
+            this.lookup = lookup;
+        }
     }
 
     public static class Profile {