diff --git a/e2e/keycloak/setup-keycloak.sh b/e2e/keycloak/setup-keycloak.sh
index 7fc46af0..ee3d3402 100755
--- a/e2e/keycloak/setup-keycloak.sh
+++ b/e2e/keycloak/setup-keycloak.sh
@@ -51,6 +51,7 @@ set -ex
     -s clientId="${CLIENT_ID}" \
     -s secret="${CLIENT_SECRET}" \
     -s "redirectUris=[\"${REDIRECT_URL}\"]" \
+    -s "attributes={\"pkce.code.challenge.method\":\"S256\"}" \
     -s consentRequired=false \
     --server "${KEYCLOAK_SERVER}" \
     --realm "${REALM}" \
diff --git a/e2e/redis/store_test.go b/e2e/redis/store_test.go
index f77db33e..88917f70 100644
--- a/e2e/redis/store_test.go
+++ b/e2e/redis/store_test.go
@@ -85,6 +85,7 @@ func TestRedisAuthorizationState(t *testing.T) {
 		State:        "state",
 		Nonce:        "nonce",
 		RequestedURL: "https://example.com",
+		CodeVerifier: "code_verifier",
 	}
 	require.NoError(t, store.SetAuthorizationState(ctx, "s1", as))
 
@@ -126,6 +127,7 @@ func TestSessionExpiration(t *testing.T) {
 			State:        "state",
 			Nonce:        "nonce",
 			RequestedURL: "https://example.com",
+			CodeVerifier: "code_verifier",
 		}
 		require.NoError(t, store.SetAuthorizationState(ctx, "s1", as))
 		require.Eventually(t, func() bool {
diff --git a/go.mod b/go.mod
index 52839f67..ed5144e8 100644
--- a/go.mod
+++ b/go.mod
@@ -15,6 +15,7 @@ require (
 	github.com/tetratelabs/run v0.3.0
 	github.com/tetratelabs/telemetry v0.8.2
 	golang.org/x/net v0.23.0
+	golang.org/x/oauth2 v0.18.0
 	google.golang.org/genproto/googleapis/rpc v0.0.0-20240304212257-790db918fca8
 	google.golang.org/grpc v1.62.1
 	google.golang.org/protobuf v1.33.0
@@ -74,7 +75,6 @@ require (
 	github.com/yuin/gopher-lua v1.1.1 // indirect
 	golang.org/x/crypto v0.21.0 // indirect
 	golang.org/x/exp v0.0.0-20240222234643-814bf88cf225 // indirect
-	golang.org/x/oauth2 v0.18.0 // indirect
 	golang.org/x/sys v0.18.0 // indirect
 	golang.org/x/term v0.18.0 // indirect
 	golang.org/x/text v0.14.0 // indirect
diff --git a/internal/authz/oidc.go b/internal/authz/oidc.go
index d5a2d8f6..ce224f3d 100644
--- a/internal/authz/oidc.go
+++ b/internal/authz/oidc.go
@@ -30,6 +30,7 @@ import (
 	typev3 "github.com/envoyproxy/go-control-plane/envoy/type/v3"
 	"github.com/lestrrat-go/jwx/v2/jws"
 	"github.com/tetratelabs/telemetry"
+	"golang.org/x/oauth2"
 	"google.golang.org/genproto/googleapis/rpc/status"
 	"google.golang.org/grpc/codes"
 
@@ -237,9 +238,10 @@ func (o *oidcHandler) redirectToIDP(ctx context.Context, log telemetry.Logger,
 	}
 
 	var (
-		sessionID = o.sessionGen.GenerateSessionID()
-		nonce     = o.sessionGen.GenerateNonce()
-		state     = o.sessionGen.GenerateState()
+		sessionID    = o.sessionGen.GenerateSessionID()
+		nonce        = o.sessionGen.GenerateNonce()
+		state        = o.sessionGen.GenerateState()
+		codeVerifier = o.sessionGen.GenerateCodeVerifier()
 	)
 
 	// Store the authorization state
@@ -251,6 +253,7 @@ func (o *oidcHandler) redirectToIDP(ctx context.Context, log telemetry.Logger,
 		State:        state,
 		Nonce:        nonce,
 		RequestedURL: requestedURL,
+		CodeVerifier: codeVerifier,
 	}); err != nil {
 		log.Error("error storing the new authorization state", err)
 		setDenyResponse(resp, newSessionErrorResponse(), codes.Unauthenticated)
@@ -259,12 +262,14 @@ func (o *oidcHandler) redirectToIDP(ctx context.Context, log telemetry.Logger,
 
 	// Generate the redirect URL
 	query := url.Values{
-		"response_type": []string{"code"},
-		"client_id":     []string{o.config.GetClientId()},
-		"redirect_uri":  []string{o.config.GetCallbackUri()},
-		"scope":         []string{strings.Join(o.config.GetScopes(), " ")},
-		"state":         []string{state},
-		"nonce":         []string{nonce},
+		"response_type":         []string{"code"},
+		"client_id":             []string{o.config.GetClientId()},
+		"redirect_uri":          []string{o.config.GetCallbackUri()},
+		"scope":                 []string{strings.Join(o.config.GetScopes(), " ")},
+		"state":                 []string{state},
+		"nonce":                 []string{nonce},
+		"code_challenge":        []string{oauth2.S256ChallengeFromVerifier(codeVerifier)},
+		"code_challenge_method": []string{"S256"},
 	}
 	redirectURL := o.config.GetAuthorizationUri() + "?" + query.Encode()
 
@@ -328,9 +333,10 @@ func (o *oidcHandler) retrieveTokens(ctx context.Context, log telemetry.Logger,
 
 	// build body
 	form := url.Values{
-		"grant_type":   []string{"authorization_code"},
-		"code":         []string{codeFromReq},
-		"redirect_uri": []string{o.config.GetCallbackUri()},
+		"grant_type":    []string{"authorization_code"},
+		"code":          []string{codeFromReq},
+		"redirect_uri":  []string{o.config.GetCallbackUri()},
+		"code_verifier": []string{stateFromStore.CodeVerifier},
 	}
 
 	// build headers
diff --git a/internal/authz/oidc_test.go b/internal/authz/oidc_test.go
index c16e5d32..e3d21a7b 100644
--- a/internal/authz/oidc_test.go
+++ b/internal/authz/oidc_test.go
@@ -34,6 +34,7 @@ import (
 	"github.com/lestrrat-go/jwx/v2/jwt"
 	"github.com/stretchr/testify/require"
 	"github.com/tetratelabs/telemetry"
+	"golang.org/x/oauth2"
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/test/bufconn"
 	"google.golang.org/protobuf/proto"
@@ -125,10 +126,11 @@ var (
 	yesterday = time.Now().Add(-24 * time.Hour)
 	tomorrow  = time.Now().Add(24 * time.Hour)
 
-	sessionID    = "test-session-id"
-	newSessionID = "new-session-id"
-	newNonce     = "new-nonce"
-	newState     = "new-state"
+	sessionID       = "test-session-id"
+	newSessionID    = "new-session-id"
+	newNonce        = "new-nonce"
+	newState        = "new-state"
+	newCodeVerifier = "new-code-verifier"
 
 	basicOIDCConfig = &oidcv1.OIDCConfig{
 		IdToken: &oidcv1.TokenConfig{
@@ -190,12 +192,14 @@ var (
 }`
 
 	wantRedirectParams = url.Values{
-		"response_type": {"code"},
-		"client_id":     {"test-client-id"},
-		"redirect_uri":  {"https://localhost:443/callback"},
-		"scope":         {"openid email"},
-		"state":         {newState},
-		"nonce":         {newNonce},
+		"response_type":         {"code"},
+		"client_id":             {"test-client-id"},
+		"redirect_uri":          {"https://localhost:443/callback"},
+		"scope":                 {"openid email"},
+		"state":                 {newState},
+		"nonce":                 {newNonce},
+		"code_challenge":        {oauth2.S256ChallengeFromVerifier(newCodeVerifier)},
+		"code_challenge_method": {"S256"},
 	}
 
 	wantRedirectBaseURI = "http://idp-test-server/auth"
@@ -228,7 +232,7 @@ func TestOIDCProcess(t *testing.T) {
 	tlsPool := internal.NewTLSConfigPool(context.Background())
 	h, err := NewOIDCHandler(basicOIDCConfig, tlsPool,
 		oidc.NewJWKSProvider(newConfigFor(basicOIDCConfig), tlsPool), sessions, clock,
-		oidc.NewStaticGenerator(newSessionID, newNonce, newState))
+		oidc.NewStaticGenerator(newSessionID, newNonce, newState, newCodeVerifier))
 	require.NoError(t, err)
 
 	ctx := context.Background()
@@ -949,7 +953,7 @@ func TestOIDCProcessWithFailingSessionStore(t *testing.T) {
 	}
 
 	h, err := NewOIDCHandler(basicOIDCConfig, tlsPool, oidc.NewJWKSProvider(newConfigFor(basicOIDCConfig), tlsPool),
-		sessions, oidc.Clock{}, oidc.NewStaticGenerator(newSessionID, newNonce, newState))
+		sessions, oidc.Clock{}, oidc.NewStaticGenerator(newSessionID, newNonce, newState, newCodeVerifier))
 	require.NoError(t, err)
 
 	ctx := context.Background()
@@ -1094,7 +1098,8 @@ func TestOIDCProcessWithFailingJWKSProvider(t *testing.T) {
 	sessions := &mockSessionStoreFactory{store: oidc.NewMemoryStore(&clock, time.Hour, time.Hour)}
 	store := sessions.Get(basicOIDCConfig)
 	tlsPool := internal.NewTLSConfigPool(context.Background())
-	h, err := NewOIDCHandler(basicOIDCConfig, tlsPool, funcJWKSProvider, sessions, clock, oidc.NewStaticGenerator(newSessionID, newNonce, newState))
+	h, err := NewOIDCHandler(basicOIDCConfig, tlsPool, funcJWKSProvider, sessions, clock,
+		oidc.NewStaticGenerator(newSessionID, newNonce, newState, newCodeVerifier))
 	require.NoError(t, err)
 
 	idpServer := newServer(wellKnownURIs)
@@ -1425,7 +1430,7 @@ func TestLoadWellKnownConfigError(t *testing.T) {
 	cfg.ConfigurationUri = "http://stopped-server/.well-known/openid-configuration"
 	sessions := &mockSessionStoreFactory{store: oidc.NewMemoryStore(&clock, time.Hour, time.Hour)}
 	_, err := NewOIDCHandler(cfg, tlsPool, oidc.NewJWKSProvider(newConfigFor(basicOIDCConfig), tlsPool),
-		sessions, clock, oidc.NewStaticGenerator(newSessionID, newNonce, newState))
+		sessions, clock, oidc.NewStaticGenerator(newSessionID, newNonce, newState, newCodeVerifier))
 	require.Error(t, err) // Fail to retrieve the dynamic config since the test server is not running
 }
 
@@ -1447,7 +1452,7 @@ func TestNewOIDCHandler(t *testing.T) {
 		t.Run(tt.name, func(t *testing.T) {
 
 			_, err := NewOIDCHandler(tt.config, tlsPool, oidc.NewJWKSProvider(newConfigFor(basicOIDCConfig), tlsPool),
-				sessions, clock, oidc.NewStaticGenerator(newSessionID, newNonce, newState))
+				sessions, clock, oidc.NewStaticGenerator(newSessionID, newNonce, newState, newCodeVerifier))
 			if tt.wantErr {
 				require.Error(t, err)
 			} else {
diff --git a/internal/oidc/redis.go b/internal/oidc/redis.go
index 6033631f..1c3a98ca 100644
--- a/internal/oidc/redis.go
+++ b/internal/oidc/redis.go
@@ -40,12 +40,13 @@ const (
 	keyState             = "state"
 	keyNonce             = "nonce"
 	keyRequestedURL      = "requested_url"
+	keyCodeVerifier      = "code_verifier"
 	keyTimeAdded         = "time_added"
 )
 
 var (
 	tokenResponseKeys      = []string{keyIDToken, keyAccessToken, keyRefreshToken, keyAccessTokenExpiry, keyTimeAdded}
-	authorizationStateKeys = []string{keyState, keyNonce, keyRequestedURL, keyTimeAdded}
+	authorizationStateKeys = []string{keyState, keyNonce, keyRequestedURL, keyTimeAdded, keyCodeVerifier}
 )
 
 // redisStore is an in-memory implementation of the SessionStore interface that stores
@@ -165,6 +166,7 @@ func (r *redisStore) SetAuthorizationState(ctx context.Context, sessionID string
 		keyState:        authorizationState.State,
 		keyNonce:        authorizationState.Nonce,
 		keyRequestedURL: authorizationState.RequestedURL,
+		keyCodeVerifier: authorizationState.CodeVerifier,
 	}
 
 	if err := r.client.HMSet(ctx, sessionID, state).Err(); err != nil {
@@ -193,7 +195,7 @@ func (r *redisStore) GetAuthorizationState(ctx context.Context, sessionID string
 		return nil, err
 	}
 
-	if state.State == "" || state.Nonce == "" || state.RequestedURL == "" {
+	if state.State == "" || state.Nonce == "" || state.RequestedURL == "" || state.CodeVerifier == "" {
 		return nil, nil
 	}
 
@@ -286,6 +288,7 @@ type (
 		State        string    `redis:"state"`
 		Nonce        string    `redis:"nonce"`
 		RequestedURL string    `redis:"requested_url"`
+		CodeVerifier string    `redis:"code_verifier"`
 		TimeAdded    time.Time `redis:"time_added"`
 	}
 )
@@ -304,5 +307,6 @@ func (r redisAuthState) AuthorizationState() *AuthorizationState {
 		State:        r.State,
 		Nonce:        r.Nonce,
 		RequestedURL: r.RequestedURL,
+		CodeVerifier: r.CodeVerifier,
 	}
 }
diff --git a/internal/oidc/redis_test.go b/internal/oidc/redis_test.go
index 89230c82..30a5f4f4 100644
--- a/internal/oidc/redis_test.go
+++ b/internal/oidc/redis_test.go
@@ -91,6 +91,7 @@ func TestRedisAuthorizationState(t *testing.T) {
 		State:        "state",
 		Nonce:        "nonce",
 		RequestedURL: "requested_url",
+		CodeVerifier: "code_verifier",
 	}
 	require.NoError(t, store.SetAuthorizationState(ctx, "s1", as))
 
diff --git a/internal/oidc/session.go b/internal/oidc/session.go
index 0d702765..6c9be37f 100644
--- a/internal/oidc/session.go
+++ b/internal/oidc/session.go
@@ -22,6 +22,7 @@ import (
 	"github.com/redis/go-redis/v9"
 	"github.com/tetratelabs/run"
 	"github.com/tetratelabs/telemetry"
+	"golang.org/x/oauth2"
 
 	configv1 "github.com/istio-ecosystem/authservice/config/gen/go/v1"
 	oidcv1 "github.com/istio-ecosystem/authservice/config/gen/go/v1/oidc"
@@ -136,6 +137,7 @@ type SessionGenerator interface {
 	GenerateSessionID() string
 	GenerateNonce() string
 	GenerateState() string
+	GenerateCodeVerifier() string
 }
 
 var (
@@ -151,9 +153,10 @@ type (
 
 	// staticGenerator is a session generator that uses static strings.
 	staticGenerator struct {
-		sessionID string
-		nonce     string
-		state     string
+		sessionID    string
+		nonce        string
+		state        string
+		codeVerifier string
 	}
 )
 
@@ -176,6 +179,10 @@ func (r randomGenerator) GenerateState() string {
 	return r.generate(32)
 }
 
+func (r randomGenerator) GenerateCodeVerifier() string {
+	return oauth2.GenerateVerifier()
+}
+
 func (r *randomGenerator) generate(n int) string {
 	const charset = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
 	b := make([]byte, n)
@@ -186,11 +193,12 @@ func (r *randomGenerator) generate(n int) string {
 }
 
 // NewStaticGenerator creates a new static session generator.
-func NewStaticGenerator(sessionID, nonce, state string) SessionGenerator {
+func NewStaticGenerator(sessionID, nonce, state, codeVerifier string) SessionGenerator {
 	return &staticGenerator{
-		sessionID: sessionID,
-		nonce:     nonce,
-		state:     state,
+		sessionID:    sessionID,
+		nonce:        nonce,
+		state:        state,
+		codeVerifier: codeVerifier,
 	}
 }
 
@@ -205,3 +213,7 @@ func (s staticGenerator) GenerateNonce() string {
 func (s staticGenerator) GenerateState() string {
 	return s.state
 }
+
+func (s staticGenerator) GenerateCodeVerifier() string {
+	return s.codeVerifier
+}
diff --git a/internal/oidc/session_test.go b/internal/oidc/session_test.go
index 35abc12f..f5a0addf 100644
--- a/internal/oidc/session_test.go
+++ b/internal/oidc/session_test.go
@@ -131,14 +131,17 @@ func TestSessionGenerator(t *testing.T) {
 		require.NotEqual(t, sg.GenerateSessionID(), sg.GenerateSessionID())
 		require.NotEqual(t, sg.GenerateState(), sg.GenerateState())
 		require.NotEqual(t, sg.GenerateNonce(), sg.GenerateNonce())
+		require.NotEqual(t, sg.GenerateCodeVerifier(), sg.GenerateCodeVerifier())
 	})
 	t.Run("static", func(t *testing.T) {
-		sg := NewStaticGenerator("sessionid", "nonce", "state")
+		sg := NewStaticGenerator("sessionid", "nonce", "state", "codeverifier")
 		require.Equal(t, sg.GenerateSessionID(), sg.GenerateSessionID())
 		require.Equal(t, sg.GenerateState(), sg.GenerateState())
 		require.Equal(t, sg.GenerateNonce(), sg.GenerateNonce())
+		require.Equal(t, sg.GenerateCodeVerifier(), sg.GenerateCodeVerifier())
 		require.Equal(t, "sessionid", sg.GenerateSessionID())
 		require.Equal(t, "state", sg.GenerateState())
 		require.Equal(t, "nonce", sg.GenerateNonce())
+		require.Equal(t, "codeverifier", sg.GenerateCodeVerifier())
 	})
 }
diff --git a/internal/oidc/state.go b/internal/oidc/state.go
index 96236e71..02b2048d 100644
--- a/internal/oidc/state.go
+++ b/internal/oidc/state.go
@@ -19,4 +19,5 @@ type AuthorizationState struct {
 	State        string
 	Nonce        string
 	RequestedURL string
+	CodeVerifier string
 }