diff --git a/CHANGELOG.md b/CHANGELOG.md
index e6d1cec..4d2eeb3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,6 @@
+## 4.3.1
+  - Added support for encoded and non encoded api-key formats on plugin configuration [#203](https://github.com/logstash-plugins/logstash-filter-elasticsearch/pull/203)
+
 ## 4.3.0
   - ES|QL support [#194](https://github.com/logstash-plugins/logstash-filter-elasticsearch/pull/194)
 
diff --git a/lib/logstash/filters/elasticsearch/client.rb b/lib/logstash/filters/elasticsearch/client.rb
index 3174550..9ac1a6f 100644
--- a/lib/logstash/filters/elasticsearch/client.rb
+++ b/lib/logstash/filters/elasticsearch/client.rb
@@ -101,12 +101,18 @@ def setup_basic_auth(user, password)
       end
 
       def setup_api_key(api_key)
-        return {} unless (api_key && api_key.value)
+        return {} unless (api_key&.value)
 
-        token = ::Base64.strict_encode64(api_key.value)
+        token = base64?(api_key.value) ? api_key.value : Base64.strict_encode64(api_key.value)
         { 'Authorization' => "ApiKey #{token}" }
       end
 
+      def base64?(string)
+        string == Base64.strict_encode64(Base64.strict_decode64(string))
+      rescue ArgumentError
+        false
+      end
+
       def get_transport_client_class
         # LS-core includes `elasticsearch` gem. The gem is composed of two separate gems: `elasticsearch-api` and `elasticsearch-transport`
         # And now `elasticsearch-transport` is old, instead we have `elastic-transport`.
diff --git a/logstash-filter-elasticsearch.gemspec b/logstash-filter-elasticsearch.gemspec
index 214b130..55c24b8 100644
--- a/logstash-filter-elasticsearch.gemspec
+++ b/logstash-filter-elasticsearch.gemspec
@@ -1,7 +1,7 @@
 Gem::Specification.new do |s|
 
   s.name            = 'logstash-filter-elasticsearch'
-  s.version         = '4.3.0'
+  s.version         = '4.3.1'
   s.licenses        = ['Apache License (2.0)']
   s.summary         = "Copies fields from previous log events in Elasticsearch to current events "
   s.description     = "This gem is a Logstash plugin required to be installed on top of the Logstash core pipeline using $LS_HOME/bin/logstash-plugin install gemname. This gem is not a stand-alone program"
diff --git a/spec/filters/elasticsearch_spec.rb b/spec/filters/elasticsearch_spec.rb
index 4c1deb4..eb219a0 100644
--- a/spec/filters/elasticsearch_spec.rb
+++ b/spec/filters/elasticsearch_spec.rb
@@ -324,14 +324,28 @@ def wait_receive_request
       end
 
       context "with ssl" do
-        let(:config) { super().merge({ 'api_key' => LogStash::Util::Password.new('foo:bar'), "ssl_enabled" => true }) }
+        let(:api_key_value) { nil }
+        let(:config) { super().merge("ssl_enabled" => true, 'api_key' => LogStash::Util::Password.new(api_key_value)) }
+        let(:encoded_api_key) { Base64.strict_encode64('foo:bar') }
 
-        it "should set authorization" do
-          plugin.register
-          client = plugin.send(:get_client).client
-          auth_header = extract_transport(client).options[:transport_options][:headers]['Authorization']
+        shared_examples "a plugin that sets the ApiKey authorization header" do
+          it "correctly sets the Authorization header" do
+            plugin.register
+            client= plugin.send(:get_client).client
+            auth_header = extract_transport(client).options[:transport_options][:headers]['Authorization']
+
+            expect(auth_header).to eql("ApiKey #{encoded_api_key}")
+          end
+        end
+
+        context "with a non-encoded API key" do
+          let(:api_key_value) { "foo:bar" }
+          it_behaves_like "a plugin that sets the ApiKey authorization header"
+        end
 
-          expect( auth_header ).to eql "ApiKey #{Base64.strict_encode64('foo:bar')}"
+        context "with an encoded API key" do
+          let(:api_key_value) { encoded_api_key }
+          it_behaves_like "a plugin that sets the ApiKey authorization header"
         end
 
         context 'user also set' do