diff --git a/config/envoyconfig/listeners.go b/config/envoyconfig/listeners.go
index ed3a24200..53cbddb65 100644
--- a/config/envoyconfig/listeners.go
+++ b/config/envoyconfig/listeners.go
@@ -340,7 +340,8 @@ func (b *Builder) buildMainHTTPConnectionManagerFilter(
 			IdleTimeout:       durationpb.New(options.IdleTimeout),
 			MaxStreamDuration: maxStreamDuration,
 		},
-		RequestTimeout: durationpb.New(options.ReadTimeout),
+		HttpProtocolOptions: http1ProtocolOptions,
+		RequestTimeout:      durationpb.New(options.ReadTimeout),
 		Tracing: &envoy_http_connection_manager.HttpConnectionManager_Tracing{
 			RandomSampling: &envoy_type_v3.Percent{Value: options.TracingSampleRate * 100},
 			Provider:       tracingProvider,
diff --git a/config/envoyconfig/listeners_test.go b/config/envoyconfig/listeners_test.go
index 44d2c4b0d..72357711c 100644
--- a/config/envoyconfig/listeners_test.go
+++ b/config/envoyconfig/listeners_test.go
@@ -742,6 +742,16 @@ func Test_buildMainHTTPConnectionManagerFilter(t *testing.T) {
 			"useRemoteAddress": true,
 			"skipXffAppend": true,
 			"xffNumTrustedHops": 1,
+			"httpProtocolOptions": {
+				"headerKeyFormat": {
+					"statefulFormatter": {
+						"name": "preserve_case",
+						"typedConfig": {
+							"@type": "type.googleapis.com/envoy.extensions.http.header_formatters.preserve_case.v3.PreserveCaseFormatterConfig"
+						}
+					}
+				}
+			},
 			"localReplyConfig":{
 				"mappers":[
 					{
diff --git a/config/envoyconfig/protocols.go b/config/envoyconfig/protocols.go
index b10dda6f0..3e34792b1 100644
--- a/config/envoyconfig/protocols.go
+++ b/config/envoyconfig/protocols.go
@@ -4,6 +4,7 @@ import (
 	"context"
 
 	envoy_config_core_v3 "github.com/envoyproxy/go-control-plane/envoy/config/core/v3"
+	envoy_extensions_http_header_formatters_preserve_case_v3 "github.com/envoyproxy/go-control-plane/envoy/extensions/http/header_formatters/preserve_case/v3"
 	envoy_extensions_upstreams_http_v3 "github.com/envoyproxy/go-control-plane/envoy/extensions/upstreams/http/v3"
 	"google.golang.org/protobuf/types/known/anypb"
 	"google.golang.org/protobuf/types/known/wrapperspb"
@@ -28,6 +29,18 @@ const (
 	initialConnectionWindowSizeLimit uint32 = 1 * 1024 * 1024
 )
 
+var http1ProtocolOptions = &envoy_config_core_v3.Http1ProtocolOptions{
+	// fix for #3935, preserve case of HTTP headers for applications that are case-sensitive
+	HeaderKeyFormat: &envoy_config_core_v3.Http1ProtocolOptions_HeaderKeyFormat{
+		HeaderFormat: &envoy_config_core_v3.Http1ProtocolOptions_HeaderKeyFormat_StatefulFormatter{
+			StatefulFormatter: &envoy_config_core_v3.TypedExtensionConfig{
+				Name:        "preserve_case",
+				TypedConfig: marshalAny(&envoy_extensions_http_header_formatters_preserve_case_v3.PreserveCaseFormatterConfig{}),
+			},
+		},
+	},
+}
+
 var http2ProtocolOptions = &envoy_config_core_v3.Http2ProtocolOptions{
 	AllowConnect:                true,
 	MaxConcurrentStreams:        wrapperspb.UInt32(maxConcurrentStreams),
@@ -35,13 +48,19 @@ var http2ProtocolOptions = &envoy_config_core_v3.Http2ProtocolOptions{
 	InitialConnectionWindowSize: wrapperspb.UInt32(initialConnectionWindowSizeLimit),
 }
 
-func buildTypedExtensionProtocolOptions(endpoints []Endpoint, upstreamProtocol upstreamProtocolConfig) map[string]*anypb.Any {
+func buildTypedExtensionProtocolOptions(
+	endpoints []Endpoint,
+	upstreamProtocol upstreamProtocolConfig,
+) map[string]*anypb.Any {
 	return map[string]*anypb.Any{
 		"envoy.extensions.upstreams.http.v3.HttpProtocolOptions": marshalAny(buildUpstreamProtocolOptions(endpoints, upstreamProtocol)),
 	}
 }
 
-func buildUpstreamProtocolOptions(endpoints []Endpoint, upstreamProtocol upstreamProtocolConfig) *envoy_extensions_upstreams_http_v3.HttpProtocolOptions {
+func buildUpstreamProtocolOptions(
+	endpoints []Endpoint,
+	upstreamProtocol upstreamProtocolConfig,
+) *envoy_extensions_upstreams_http_v3.HttpProtocolOptions {
 	switch upstreamProtocol {
 	case upstreamProtocolHTTP2:
 		// when explicitly configured, force HTTP/2
@@ -66,6 +85,7 @@ func buildUpstreamProtocolOptions(endpoints []Endpoint, upstreamProtocol upstrea
 			return &envoy_extensions_upstreams_http_v3.HttpProtocolOptions{
 				UpstreamProtocolOptions: &envoy_extensions_upstreams_http_v3.HttpProtocolOptions_AutoConfig{
 					AutoConfig: &envoy_extensions_upstreams_http_v3.HttpProtocolOptions_AutoHttpConfig{
+						HttpProtocolOptions:  http1ProtocolOptions,
 						Http2ProtocolOptions: http2ProtocolOptions,
 					},
 				},
@@ -78,7 +98,7 @@ func buildUpstreamProtocolOptions(endpoints []Endpoint, upstreamProtocol upstrea
 		UpstreamProtocolOptions: &envoy_extensions_upstreams_http_v3.HttpProtocolOptions_ExplicitHttpConfig_{
 			ExplicitHttpConfig: &envoy_extensions_upstreams_http_v3.HttpProtocolOptions_ExplicitHttpConfig{
 				ProtocolConfig: &envoy_extensions_upstreams_http_v3.HttpProtocolOptions_ExplicitHttpConfig_HttpProtocolOptions{
-					HttpProtocolOptions: &envoy_config_core_v3.Http1ProtocolOptions{},
+					HttpProtocolOptions: http1ProtocolOptions,
 				},
 			},
 		},
diff --git a/config/envoyconfig/protocols_test.go b/config/envoyconfig/protocols_test.go
new file mode 100644
index 000000000..f25bb6852
--- /dev/null
+++ b/config/envoyconfig/protocols_test.go
@@ -0,0 +1,36 @@
+package envoyconfig
+
+import (
+	"testing"
+
+	envoy_config_core_v3 "github.com/envoyproxy/go-control-plane/envoy/config/core/v3"
+	envoy_extensions_http_header_formatters_preserve_case_v3 "github.com/envoyproxy/go-control-plane/envoy/extensions/http/header_formatters/preserve_case/v3"
+	envoy_extensions_upstreams_http_v3 "github.com/envoyproxy/go-control-plane/envoy/extensions/upstreams/http/v3"
+	"github.com/google/go-cmp/cmp"
+	"github.com/stretchr/testify/assert"
+	"google.golang.org/protobuf/testing/protocmp"
+)
+
+func Test_buildUpstreamProtocolOptions(t *testing.T) {
+	t.Parallel()
+
+	assert.Empty(t,
+		cmp.Diff(&envoy_extensions_upstreams_http_v3.HttpProtocolOptions{
+			UpstreamProtocolOptions: &envoy_extensions_upstreams_http_v3.HttpProtocolOptions_ExplicitHttpConfig_{
+				ExplicitHttpConfig: &envoy_extensions_upstreams_http_v3.HttpProtocolOptions_ExplicitHttpConfig{
+					ProtocolConfig: &envoy_extensions_upstreams_http_v3.HttpProtocolOptions_ExplicitHttpConfig_HttpProtocolOptions{
+						HttpProtocolOptions: &envoy_config_core_v3.Http1ProtocolOptions{
+							HeaderKeyFormat: &envoy_config_core_v3.Http1ProtocolOptions_HeaderKeyFormat{
+								HeaderFormat: &envoy_config_core_v3.Http1ProtocolOptions_HeaderKeyFormat_StatefulFormatter{
+									StatefulFormatter: &envoy_config_core_v3.TypedExtensionConfig{
+										Name:        "preserve_case",
+										TypedConfig: marshalAny(&envoy_extensions_http_header_formatters_preserve_case_v3.PreserveCaseFormatterConfig{}),
+									},
+								},
+							},
+						},
+					},
+				},
+			},
+		}, buildUpstreamProtocolOptions(nil, upstreamProtocolHTTP1), protocmp.Transform()))
+}