diff --git a/pkg/client/client.go b/pkg/client/client.go
index f6a407b..7486ef1 100644
--- a/pkg/client/client.go
+++ b/pkg/client/client.go
@@ -48,11 +48,11 @@ type TokenEndpointCaller interface {
 	HttpClient() *http.Client
 }
 
-func CallTokenEndpoint(request interface{}, caller TokenEndpointCaller) (newToken *oauth2.Token, err error) {
+func CallTokenEndpoint(request any, caller TokenEndpointCaller) (newToken *oauth2.Token, err error) {
 	return callTokenEndpoint(request, nil, caller)
 }
 
-func callTokenEndpoint(request interface{}, authFn interface{}, caller TokenEndpointCaller) (newToken *oauth2.Token, err error) {
+func callTokenEndpoint(request any, authFn any, caller TokenEndpointCaller) (newToken *oauth2.Token, err error) {
 	req, err := httphelper.FormRequest(caller.TokenEndpoint(), request, Encoder, authFn)
 	if err != nil {
 		return nil, err
@@ -80,7 +80,7 @@ type EndSessionCaller interface {
 	HttpClient() *http.Client
 }
 
-func CallEndSessionEndpoint(request interface{}, authFn interface{}, caller EndSessionCaller) (*url.URL, error) {
+func CallEndSessionEndpoint(request any, authFn any, caller EndSessionCaller) (*url.URL, error) {
 	req, err := httphelper.FormRequest(caller.GetEndSessionEndpoint(), request, Encoder, authFn)
 	if err != nil {
 		return nil, err
@@ -123,7 +123,7 @@ type RevokeRequest struct {
 	ClientSecret  string `schema:"client_secret"`
 }
 
-func CallRevokeEndpoint(request interface{}, authFn interface{}, caller RevokeCaller) error {
+func CallRevokeEndpoint(request any, authFn any, caller RevokeCaller) error {
 	req, err := httphelper.FormRequest(caller.GetRevokeEndpoint(), request, Encoder, authFn)
 	if err != nil {
 		return err
@@ -151,7 +151,7 @@ func CallRevokeEndpoint(request interface{}, authFn interface{}, caller RevokeCa
 	return nil
 }
 
-func CallTokenExchangeEndpoint(request interface{}, authFn interface{}, caller TokenEndpointCaller) (resp *oidc.TokenExchangeResponse, err error) {
+func CallTokenExchangeEndpoint(request any, authFn any, caller TokenEndpointCaller) (resp *oidc.TokenExchangeResponse, err error) {
 	req, err := httphelper.FormRequest(caller.TokenEndpoint(), request, Encoder, authFn)
 	if err != nil {
 		return nil, err
diff --git a/pkg/client/rs/resource_server.go b/pkg/client/rs/resource_server.go
index c641940..95b6e2e 100644
--- a/pkg/client/rs/resource_server.go
+++ b/pkg/client/rs/resource_server.go
@@ -15,7 +15,7 @@ type ResourceServer interface {
 	IntrospectionURL() string
 	TokenEndpoint() string
 	HttpClient() *http.Client
-	AuthFn() (interface{}, error)
+	AuthFn() (any, error)
 }
 
 type resourceServer struct {
@@ -23,7 +23,7 @@ type resourceServer struct {
 	tokenURL      string
 	introspectURL string
 	httpClient    *http.Client
-	authFn        func() (interface{}, error)
+	authFn        func() (any, error)
 }
 
 func (r *resourceServer) IntrospectionURL() string {
@@ -38,12 +38,12 @@ func (r *resourceServer) HttpClient() *http.Client {
 	return r.httpClient
 }
 
-func (r *resourceServer) AuthFn() (interface{}, error) {
+func (r *resourceServer) AuthFn() (any, error) {
 	return r.authFn()
 }
 
 func NewResourceServerClientCredentials(issuer, clientID, clientSecret string, option ...Option) (ResourceServer, error) {
-	authorizer := func() (interface{}, error) {
+	authorizer := func() (any, error) {
 		return httphelper.AuthorizeBasic(clientID, clientSecret), nil
 	}
 	return newResourceServer(issuer, authorizer, option...)
@@ -54,7 +54,7 @@ func NewResourceServerJWTProfile(issuer, clientID, keyID string, key []byte, opt
 	if err != nil {
 		return nil, err
 	}
-	authorizer := func() (interface{}, error) {
+	authorizer := func() (any, error) {
 		assertion, err := client.SignedJWTProfileAssertion(clientID, []string{issuer}, time.Hour, signer)
 		if err != nil {
 			return nil, err
@@ -64,7 +64,7 @@ func NewResourceServerJWTProfile(issuer, clientID, keyID string, key []byte, opt
 	return newResourceServer(issuer, authorizer, options...)
 }
 
-func newResourceServer(issuer string, authorizer func() (interface{}, error), options ...Option) (*resourceServer, error) {
+func newResourceServer(issuer string, authorizer func() (any, error), options ...Option) (*resourceServer, error) {
 	rs := &resourceServer{
 		issuer:     issuer,
 		httpClient: httphelper.DefaultHTTPClient,
diff --git a/pkg/client/rs/resource_server_test.go b/pkg/client/rs/resource_server_test.go
index b5fb496..16cb6ad 100644
--- a/pkg/client/rs/resource_server_test.go
+++ b/pkg/client/rs/resource_server_test.go
@@ -11,14 +11,14 @@ import (
 func TestNewResourceServer(t *testing.T) {
 	type args struct {
 		issuer     string
-		authorizer func() (interface{}, error)
+		authorizer func() (any, error)
 		options    []Option
 	}
 	type wantFields struct {
 		issuer        string
 		tokenURL      string
 		introspectURL string
-		authFn        func() (interface{}, error)
+		authFn        func() (any, error)
 	}
 	tests := []struct {
 		name       string
diff --git a/pkg/client/tokenexchange/tokenexchange.go b/pkg/client/tokenexchange/tokenexchange.go
index 1375f68..4ae5507 100644
--- a/pkg/client/tokenexchange/tokenexchange.go
+++ b/pkg/client/tokenexchange/tokenexchange.go
@@ -12,13 +12,13 @@ import (
 type TokenExchanger interface {
 	TokenEndpoint() string
 	HttpClient() *http.Client
-	AuthFn() (interface{}, error)
+	AuthFn() (any, error)
 }
 
 type OAuthTokenExchange struct {
 	httpClient    *http.Client
 	tokenEndpoint string
-	authFn        func() (interface{}, error)
+	authFn        func() (any, error)
 }
 
 func NewTokenExchanger(issuer string, options ...func(source *OAuthTokenExchange)) (TokenExchanger, error) {
@@ -26,13 +26,13 @@ func NewTokenExchanger(issuer string, options ...func(source *OAuthTokenExchange
 }
 
 func NewTokenExchangerClientCredentials(issuer, clientID, clientSecret string, options ...func(source *OAuthTokenExchange)) (TokenExchanger, error) {
-	authorizer := func() (interface{}, error) {
+	authorizer := func() (any, error) {
 		return httphelper.AuthorizeBasic(clientID, clientSecret), nil
 	}
 	return newOAuthTokenExchange(issuer, authorizer, options...)
 }
 
-func newOAuthTokenExchange(issuer string, authorizer func() (interface{}, error), options ...func(source *OAuthTokenExchange)) (*OAuthTokenExchange, error) {
+func newOAuthTokenExchange(issuer string, authorizer func() (any, error), options ...func(source *OAuthTokenExchange)) (*OAuthTokenExchange, error) {
 	te := &OAuthTokenExchange{
 		httpClient: httphelper.DefaultHTTPClient,
 	}
@@ -78,7 +78,7 @@ func (te *OAuthTokenExchange) HttpClient() *http.Client {
 	return te.httpClient
 }
 
-func (te *OAuthTokenExchange) AuthFn() (interface{}, error) {
+func (te *OAuthTokenExchange) AuthFn() (any, error) {
 	if te.authFn != nil {
 		return te.authFn()
 	}