diff --git a/pkg/handler/handler.go b/pkg/handler/handler.go
index ec7e966..7550604 100644
--- a/pkg/handler/handler.go
+++ b/pkg/handler/handler.go
@@ -143,7 +143,7 @@ func (s *Standalone) Login(w http.ResponseWriter, r *http.Request) {
 		"redirect_after_login": canonicalRedirect,
 	}
 	mw.LogEntryFrom(r).WithFields(fields).Info("login: redirecting to identity provider")
-	http.Redirect(w, r, login.AuthCodeURL(), http.StatusFound)
+	http.Redirect(w, r, login.AuthCodeURL, http.StatusFound)
 }
 
 func (s *Standalone) LoginCallback(w http.ResponseWriter, r *http.Request) {
diff --git a/pkg/mock/openid.go b/pkg/mock/openid.go
index 99b6e0e..138add0 100644
--- a/pkg/mock/openid.go
+++ b/pkg/mock/openid.go
@@ -16,13 +16,12 @@ import (
 	"github.com/lestrrat-go/jwx/v2/jwa"
 	"github.com/lestrrat-go/jwx/v2/jwk"
 	"github.com/lestrrat-go/jwx/v2/jwt"
+	"golang.org/x/oauth2"
 
 	"github.com/nais/wonderwall/pkg/config"
 	"github.com/nais/wonderwall/pkg/cookie"
 	"github.com/nais/wonderwall/pkg/crypto"
 	handlerpkg "github.com/nais/wonderwall/pkg/handler"
-	"github.com/nais/wonderwall/pkg/openid"
-	openidclient "github.com/nais/wonderwall/pkg/openid/client"
 	openidconfig "github.com/nais/wonderwall/pkg/openid/config"
 	scopespkg "github.com/nais/wonderwall/pkg/openid/scopes"
 	"github.com/nais/wonderwall/pkg/router"
@@ -311,7 +310,7 @@ func (ip *IdentityProviderHandler) Token(w http.ResponseWriter, r *http.Request)
 		return
 	}
 
-	grantType := r.PostForm.Get(openid.GrantType)
+	grantType := r.PostForm.Get("grant_type")
 	switch grantType {
 	case "authorization_code":
 		ip.TokenCodeGrant(w, r)
@@ -373,7 +372,7 @@ func (ip *IdentityProviderHandler) TokenCodeGrant(w http.ResponseWriter, r *http
 		return
 	}
 
-	expectedCodeChallenge := openidclient.CodeChallenge(codeVerifier)
+	expectedCodeChallenge := oauth2.S256ChallengeFromVerifier(codeVerifier)
 
 	if expectedCodeChallenge != auth.CodeChallenge {
 		w.WriteHeader(http.StatusBadRequest)
diff --git a/pkg/openid/client/client.go b/pkg/openid/client/client.go
index 6220c59..b628ca2 100644
--- a/pkg/openid/client/client.go
+++ b/pkg/openid/client/client.go
@@ -146,17 +146,19 @@ func (c *Client) RefreshGrant(ctx context.Context, refreshToken string) (*openid
 	}
 
 	v := url.Values{}
-	v.Set(openid.GrantType, openid.RefreshTokenValue)
-	v.Set(openid.RefreshToken, refreshToken)
-	v.Set(openid.ClientID, c.cfg.Client().ClientID())
-	v.Set(openid.ClientAssertion, assertion)
-	v.Set(openid.ClientAssertionType, openid.ClientAssertionTypeJwtBearer)
+	v.Set("grant_type", "refresh_token")
+	v.Set("refresh_token", refreshToken)
+	v.Set("client_id", c.cfg.Client().ClientID())
+
+	for key, val := range openid.JwtAuthenticationParameters(assertion) {
+		v.Set(key, val)
+	}
 
 	r, err := http.NewRequestWithContext(ctx, http.MethodPost, c.cfg.Provider().TokenEndpoint(), strings.NewReader(v.Encode()))
 	if err != nil {
 		return nil, fmt.Errorf("creating request: %w", err)
 	}
-	r.Header.Add("Content-Type", "application/x-www-form-urlencoded")
+	r.Header.Set("Content-Type", "application/x-www-form-urlencoded")
 
 	resp, err := c.httpClient.Do(r)
 	if err != nil {
@@ -186,15 +188,3 @@ func (c *Client) RefreshGrant(ctx context.Context, refreshToken string) (*openid
 
 	return &tokenResponse, nil
 }
-
-func StateMismatchError(expectedState, actualState string) error {
-	if len(actualState) <= 0 {
-		return fmt.Errorf("missing state parameter in request (possible csrf)")
-	}
-
-	if expectedState != actualState {
-		return fmt.Errorf("state parameter mismatch (possible csrf): expected %s, got %s", expectedState, actualState)
-	}
-
-	return nil
-}
diff --git a/pkg/openid/client/client_test.go b/pkg/openid/client/client_test.go
index 15c3ec8..b6828e3 100644
--- a/pkg/openid/client/client_test.go
+++ b/pkg/openid/client/client_test.go
@@ -45,22 +45,6 @@ func TestMakeAssertion(t *testing.T) {
 	assert.True(t, assertion.Expiration().Before(time.Now().Add(expiry)))
 }
 
-func TestStateMismatchError(t *testing.T) {
-	for _, tt := range []struct {
-		name, expected, actual string
-		assertion              assert.ErrorAssertionFunc
-	}{
-		{"missing actual state", "expected", "", assert.Error},
-		{"state mismatch", "match", "not-match", assert.Error},
-		{"state match", "match", "match", assert.NoError},
-	} {
-		t.Run(tt.name, func(t *testing.T) {
-			err := client.StateMismatchError(tt.expected, tt.actual)
-			tt.assertion(t, err)
-		})
-	}
-}
-
 func newTestClientWithConfig(config *mock.TestConfiguration) *client.Client {
 	jwksProvider := mock.NewTestJwksProvider()
 	return client.NewClient(config, jwksProvider)
diff --git a/pkg/openid/client/login.go b/pkg/openid/client/login.go
index 323fe0a..22e25ea 100644
--- a/pkg/openid/client/login.go
+++ b/pkg/openid/client/login.go
@@ -1,8 +1,6 @@
 package client
 
 import (
-	"crypto/sha256"
-	"encoding/base64"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -10,21 +8,17 @@ import (
 
 	"golang.org/x/oauth2"
 
-	pkgcfg "github.com/nais/wonderwall/pkg/config"
+	cfg "github.com/nais/wonderwall/pkg/config"
 	"github.com/nais/wonderwall/pkg/cookie"
 	"github.com/nais/wonderwall/pkg/crypto"
 	"github.com/nais/wonderwall/pkg/openid"
 	"github.com/nais/wonderwall/pkg/strings"
-	urlpkg "github.com/nais/wonderwall/pkg/url"
+	"github.com/nais/wonderwall/pkg/url"
 )
 
 const (
 	LocaleURLParameter        = "locale"
 	SecurityLevelURLParameter = "level"
-
-	ResponseModeQuery = "query"
-
-	CodeChallengeMethodS256 = "S256"
 )
 
 var (
@@ -34,13 +28,13 @@ var (
 
 	// LoginParameterMapping maps incoming login parameters to OpenID Connect parameters
 	LoginParameterMapping = map[string]string{
-		LocaleURLParameter:        openid.UILocales,
-		SecurityLevelURLParameter: openid.ACRValues,
+		LocaleURLParameter:        "ui_locales",
+		SecurityLevelURLParameter: "acr_values",
 	}
 )
 
 func NewLogin(c *Client, r *http.Request) (*Login, error) {
-	callbackURL, err := urlpkg.LoginCallback(r)
+	callbackURL, err := url.LoginCallback(r)
 	if err != nil {
 		return nil, fmt.Errorf("generating callback url: %w", err)
 	}
@@ -55,22 +49,27 @@ func NewLogin(c *Client, r *http.Request) (*Login, error) {
 		return nil, fmt.Errorf("%w: %w", ErrInvalidLocale, err)
 	}
 
-	params, err := newLoginParameters(acr, callbackURL)
+	nonce, err := strings.GenerateBase64(32)
 	if err != nil {
-		return nil, fmt.Errorf("generating parameters: %w", err)
+		return nil, fmt.Errorf("creating nonce: %w", err)
 	}
 
+	state, err := strings.GenerateBase64(32)
+	if err != nil {
+		return nil, fmt.Errorf("creating state: %w", err)
+	}
+
+	codeVerifier := oauth2.GenerateVerifier()
+
 	opts := []oauth2.AuthCodeOption{
-		oauth2.SetAuthURLParam(openid.Nonce, params.Nonce),
-		oauth2.SetAuthURLParam(openid.ResponseMode, ResponseModeQuery),
-		oauth2.SetAuthURLParam(openid.CodeChallenge, params.CodeChallenge),
-		oauth2.SetAuthURLParam(openid.CodeChallengeMethod, CodeChallengeMethodS256),
-		oauth2.SetAuthURLParam(openid.RedirectURI, callbackURL),
+		oauth2.SetAuthURLParam("nonce", nonce),
+		oauth2.SetAuthURLParam("response_mode", "query"),
+		oauth2.S256ChallengeOption(codeVerifier),
+		openid.RedirectURIOption(callbackURL),
 	}
 
-	resourceIndicator := c.cfg.Client().ResourceIndicator()
-	if resourceIndicator != "" {
-		opts = append(opts, oauth2.SetAuthURLParam(openid.Resource, resourceIndicator))
+	if resource := c.cfg.Client().ResourceIndicator(); resource != "" {
+		opts = append(opts, oauth2.SetAuthURLParam("resource", resource))
 	}
 
 	if len(acr) > 0 {
@@ -82,42 +81,26 @@ func NewLogin(c *Client, r *http.Request) (*Login, error) {
 	}
 
 	return &Login{
-		authCodeURL: c.oauth2Config.AuthCodeURL(params.State, opts...),
-		cookie:      params.cookie(),
-		params:      params,
+		AuthCodeURL: c.oauth2Config.AuthCodeURL(state, opts...),
+		LoginCookie: &openid.LoginCookie{
+			Acr:          acr,
+			CodeVerifier: codeVerifier,
+			State:        state,
+			Nonce:        nonce,
+			RedirectURI:  callbackURL,
+		},
 	}, nil
 }
 
 type Login struct {
-	authCodeURL string
-	cookie      *openid.LoginCookie
-	params      *loginParameters
-}
-
-func (l *Login) AuthCodeURL() string {
-	return l.authCodeURL
-}
-
-func (l *Login) CodeChallenge() string {
-	return l.params.CodeChallenge
-}
-
-func (l *Login) CodeVerifier() string {
-	return l.params.CodeVerifier
-}
-
-func (l *Login) Nonce() string {
-	return l.params.Nonce
-}
-
-func (l *Login) State() string {
-	return l.params.State
+	AuthCodeURL string
+	*openid.LoginCookie
 }
 
 func (l *Login) SetCookie(w http.ResponseWriter, opts cookie.Options, crypter crypto.Crypter, canonicalRedirect string) error {
-	l.cookie.Referer = canonicalRedirect
+	l.LoginCookie.Referer = canonicalRedirect
 
-	loginCookieJson, err := json.Marshal(l.cookie)
+	loginCookieJson, err := json.Marshal(l.LoginCookie)
 	if err != nil {
 		return fmt.Errorf("marshalling login cookie: %w", err)
 	}
@@ -138,51 +121,6 @@ func (l *Login) SetCookie(w http.ResponseWriter, opts cookie.Options, crypter cr
 	return nil
 }
 
-type loginParameters struct {
-	Acr           string
-	CodeVerifier  string
-	CodeChallenge string
-	Nonce         string
-	RedirectURI   string
-	State         string
-}
-
-func newLoginParameters(acr, redirectUri string) (*loginParameters, error) {
-	codeVerifier, err := strings.GenerateBase64(64)
-	if err != nil {
-		return nil, fmt.Errorf("creating code verifier: %w", err)
-	}
-
-	nonce, err := strings.GenerateBase64(32)
-	if err != nil {
-		return nil, fmt.Errorf("creating nonce: %w", err)
-	}
-
-	state, err := strings.GenerateBase64(32)
-	if err != nil {
-		return nil, fmt.Errorf("creating state: %w", err)
-	}
-
-	return &loginParameters{
-		Acr:           acr,
-		CodeVerifier:  codeVerifier,
-		CodeChallenge: CodeChallenge(codeVerifier),
-		Nonce:         nonce,
-		RedirectURI:   redirectUri,
-		State:         state,
-	}, nil
-}
-
-func (in *loginParameters) cookie() *openid.LoginCookie {
-	return &openid.LoginCookie{
-		Acr:          in.Acr,
-		State:        in.State,
-		Nonce:        in.Nonce,
-		CodeVerifier: in.CodeVerifier,
-		RedirectURI:  in.RedirectURI,
-	}
-}
-
 func getAcrParam(c *Client, r *http.Request) (string, error) {
 	defaultValue := c.cfg.Client().ACRValues()
 	if len(defaultValue) == 0 {
@@ -199,7 +137,7 @@ func getAcrParam(c *Client, r *http.Request) (string, error) {
 		return paramValue, nil
 	}
 
-	translatedAcr, ok := pkgcfg.IDPortenAcrMapping[paramValue]
+	translatedAcr, ok := cfg.IDPortenAcrMapping[paramValue]
 	if ok && supported.Contains(translatedAcr) {
 		return translatedAcr, nil
 	}
@@ -225,11 +163,3 @@ func getLocaleParam(c *Client, r *http.Request) (string, error) {
 
 	return "", fmt.Errorf("%w: invalid value for %s=%s (must be one of '%s')", ErrInvalidLoginParameter, LocaleURLParameter, paramValue, supported)
 }
-
-func CodeChallenge(codeVerifier string) string {
-	hasher := sha256.New()
-	hasher.Write([]byte(codeVerifier))
-	codeVerifierHash := hasher.Sum(nil)
-
-	return base64.RawURLEncoding.EncodeToString(codeVerifierHash)
-}
diff --git a/pkg/openid/client/login_callback.go b/pkg/openid/client/login_callback.go
index e6b80b5..c5744c3 100644
--- a/pkg/openid/client/login_callback.go
+++ b/pkg/openid/client/login_callback.go
@@ -41,9 +41,9 @@ func NewLoginCallback(c *Client, r *http.Request, cookie *openid.LoginCookie) (*
 }
 
 func (in *LoginCallback) IdentityProviderError() error {
-	if in.requestParams.Get(openid.Error) != "" {
-		oauthError := in.requestParams.Get(openid.Error)
-		oauthErrorDescription := in.requestParams.Get(openid.ErrorDescription)
+	if in.requestParams.Get("error") != "" {
+		oauthError := in.requestParams.Get("error")
+		oauthErrorDescription := in.requestParams.Get("error_description")
 		return fmt.Errorf("error from identity provider: %s: %s", oauthError, oauthErrorDescription)
 	}
 
@@ -51,10 +51,7 @@ func (in *LoginCallback) IdentityProviderError() error {
 }
 
 func (in *LoginCallback) StateMismatchError() error {
-	expectedState := in.cookie.State
-	actualState := in.requestParams.Get(openid.State)
-
-	return StateMismatchError(expectedState, actualState)
+	return openid.StateMismatchError(in.requestParams, in.cookie.State)
 }
 
 func (in *LoginCallback) RedeemTokens(ctx context.Context) (*openid.Tokens, error) {
@@ -64,13 +61,12 @@ func (in *LoginCallback) RedeemTokens(ctx context.Context) (*openid.Tokens, erro
 	}
 
 	opts := []oauth2.AuthCodeOption{
-		oauth2.SetAuthURLParam(openid.CodeVerifier, in.cookie.CodeVerifier),
-		oauth2.SetAuthURLParam(openid.ClientAssertion, clientAssertion),
-		oauth2.SetAuthURLParam(openid.ClientAssertionType, openid.ClientAssertionTypeJwtBearer),
-		oauth2.SetAuthURLParam(openid.RedirectURI, in.cookie.RedirectURI),
+		openid.RedirectURIOption(in.cookie.RedirectURI),
+		oauth2.VerifierOption(in.cookie.CodeVerifier),
 	}
+	opts = openid.WithJwtAuthentication(opts, clientAssertion)
 
-	code := in.requestParams.Get(openid.Code)
+	code := in.requestParams.Get("code")
 	rawTokens, err := in.AuthCodeGrant(ctx, code, opts)
 	if err != nil {
 		return nil, fmt.Errorf("exchanging authorization code for token: %w", err)
diff --git a/pkg/openid/client/login_callback_test.go b/pkg/openid/client/login_callback_test.go
index adcda26..a3ee016 100644
--- a/pkg/openid/client/login_callback_test.go
+++ b/pkg/openid/client/login_callback_test.go
@@ -6,6 +6,7 @@ import (
 	"time"
 
 	"github.com/stretchr/testify/assert"
+	"golang.org/x/oauth2"
 
 	"github.com/nais/wonderwall/pkg/mock"
 	"github.com/nais/wonderwall/pkg/openid"
@@ -132,7 +133,7 @@ func newLoginCallback(t *testing.T, url string) (*mock.IdentityProvider, *client
 		"some-code": {
 			AcrLevel:      "some-acr",
 			ClientID:      idp.OpenIDConfig.Client().ClientID(),
-			CodeChallenge: client.CodeChallenge("some-verifier"),
+			CodeChallenge: oauth2.S256ChallengeFromVerifier("some-verifier"),
 			Nonce:         "some-nonce",
 			RedirectUri:   redirect,
 		},
diff --git a/pkg/openid/client/login_test.go b/pkg/openid/client/login_test.go
index 7f014ae..e0d6fdc 100644
--- a/pkg/openid/client/login_test.go
+++ b/pkg/openid/client/login_test.go
@@ -7,6 +7,7 @@ import (
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+	"golang.org/x/oauth2"
 
 	"github.com/nais/wonderwall/pkg/mock"
 	"github.com/nais/wonderwall/pkg/openid/client"
@@ -126,7 +127,7 @@ func TestLogin_URL(t *testing.T) {
 			} else {
 				require.NoError(t, err)
 
-				parsed, err := url.Parse(result.AuthCodeURL())
+				parsed, err := url.Parse(result.AuthCodeURL)
 				assert.NoError(t, err)
 
 				query := parsed.Query()
@@ -148,13 +149,11 @@ func TestLogin_URL(t *testing.T) {
 				assert.ElementsMatch(t, query["client_id"], []string{openidConfig.Client().ClientID()})
 				assert.ElementsMatch(t, query["redirect_uri"], []string{callbackURL})
 				assert.ElementsMatch(t, query["scope"], []string{openidConfig.Client().Scopes().String()})
-				assert.ElementsMatch(t, query["state"], []string{result.State()})
-				assert.ElementsMatch(t, query["nonce"], []string{result.Nonce()})
+				assert.ElementsMatch(t, query["state"], []string{result.State})
+				assert.ElementsMatch(t, query["nonce"], []string{result.Nonce})
 				assert.ElementsMatch(t, query["response_mode"], []string{"query"})
-				assert.ElementsMatch(t, query["code_challenge"], []string{result.CodeChallenge()})
 				assert.ElementsMatch(t, query["code_challenge_method"], []string{"S256"})
-
-				assert.Equal(t, client.CodeChallenge(result.CodeVerifier()), result.CodeChallenge())
+				assert.ElementsMatch(t, query["code_challenge"], []string{oauth2.S256ChallengeFromVerifier(result.CodeVerifier)})
 
 				if test.extraParams != nil {
 					for key, value := range test.extraParams {
@@ -187,7 +186,7 @@ func TestLoginURL_WithResourceIndicator(t *testing.T) {
 	result, err := c.Login(req)
 	assert.NoError(t, err)
 	assert.NotEmpty(t, result)
-	parsed, err := url.Parse(result.AuthCodeURL())
+	parsed, err := url.Parse(result.AuthCodeURL)
 	assert.NoError(t, err)
 
 	query := parsed.Query()
diff --git a/pkg/openid/client/logout.go b/pkg/openid/client/logout.go
index b7b32ec..f63284e 100644
--- a/pkg/openid/client/logout.go
+++ b/pkg/openid/client/logout.go
@@ -43,11 +43,11 @@ func NewLogout(c *Client, r *http.Request) (*Logout, error) {
 func (in *Logout) SingleLogoutURL(idToken string) string {
 	endSessionEndpoint := in.cfg.Provider().EndSessionEndpointURL()
 	v := endSessionEndpoint.Query()
-	v.Add(openid.PostLogoutRedirectURI, in.logoutCallbackURL)
-	v.Add(openid.State, in.Cookie.State)
+	v.Set("post_logout_redirect_uri", in.logoutCallbackURL)
+	v.Set("state", in.Cookie.State)
 
 	if len(idToken) > 0 {
-		v.Add(openid.IDTokenHint, idToken)
+		v.Set("id_token_hint", idToken)
 	}
 
 	endSessionEndpoint.RawQuery = v.Encode()
diff --git a/pkg/openid/client/logout_callback.go b/pkg/openid/client/logout_callback.go
index b4e1684..8fa8b4f 100644
--- a/pkg/openid/client/logout_callback.go
+++ b/pkg/openid/client/logout_callback.go
@@ -47,8 +47,5 @@ func (in *LogoutCallback) stateMismatchError() error {
 		return fmt.Errorf("logout cookie is nil")
 	}
 
-	expectedState := in.cookie.State
-	actualState := in.request.URL.Query().Get(openid.State)
-
-	return StateMismatchError(expectedState, actualState)
+	return openid.StateMismatchError(in.request.URL.Query(), in.cookie.State)
 }
diff --git a/pkg/openid/client/logout_frontchannel.go b/pkg/openid/client/logout_frontchannel.go
index c3f4a93..ac0fe46 100644
--- a/pkg/openid/client/logout_frontchannel.go
+++ b/pkg/openid/client/logout_frontchannel.go
@@ -2,8 +2,6 @@ package client
 
 import (
 	"net/http"
-
-	"github.com/nais/wonderwall/pkg/openid"
 )
 
 type LogoutFrontchannel struct {
@@ -12,7 +10,7 @@ type LogoutFrontchannel struct {
 
 func NewLogoutFrontchannel(r *http.Request) *LogoutFrontchannel {
 	params := r.URL.Query()
-	sid := params.Get(openid.Sid)
+	sid := params.Get("sid")
 
 	return &LogoutFrontchannel{
 		sid: sid,
diff --git a/pkg/openid/oauth2.go b/pkg/openid/oauth2.go
new file mode 100644
index 0000000..8a398ac
--- /dev/null
+++ b/pkg/openid/oauth2.go
@@ -0,0 +1,56 @@
+package openid
+
+import (
+	"fmt"
+	"net/url"
+
+	"golang.org/x/oauth2"
+)
+
+// TokenResponse is the struct representing the HTTP response from authorization servers as defined in RFC 6749, section 5.1.
+type TokenResponse struct {
+	AccessToken  string `json:"access_token"`
+	ExpiresIn    int64  `json:"expires_in"`
+	RefreshToken string `json:"refresh_token"`
+	TokenType    string `json:"token_type"`
+}
+
+// TokenErrorResponse is the struct representing the HTTP error response returned from authorization servers as defined in RFC 6749, section 5.2.
+type TokenErrorResponse struct {
+	Error            string `json:"error"`
+	ErrorDescription string `json:"error_description"`
+}
+
+// JwtAuthenticationParameters returns a map of parameters to be sent to the authorization server when using a JWT for client authentication in RFC 7523, section 2.2.
+func JwtAuthenticationParameters(clientAssertion string) map[string]string {
+	return map[string]string{
+		"client_assertion":      clientAssertion,
+		"client_assertion_type": "urn:ietf:params:oauth:client-assertion-type:jwt-bearer",
+	}
+}
+
+func WithJwtAuthentication(opts []oauth2.AuthCodeOption, clientAssertion string) []oauth2.AuthCodeOption {
+	for k, v := range JwtAuthenticationParameters(clientAssertion) {
+		opts = append(opts, oauth2.SetAuthURLParam(k, v))
+	}
+
+	return opts
+}
+
+func RedirectURIOption(redirectUri string) oauth2.AuthCodeOption {
+	return oauth2.SetAuthURLParam("redirect_uri", redirectUri)
+}
+
+func StateMismatchError(queryParams url.Values, expectedState string) error {
+	actualState := queryParams.Get("state")
+
+	if len(actualState) <= 0 {
+		return fmt.Errorf("missing state parameter in request (possible csrf)")
+	}
+
+	if expectedState != actualState {
+		return fmt.Errorf("state parameter mismatch (possible csrf): expected %s, got %s", expectedState, actualState)
+	}
+
+	return nil
+}
diff --git a/pkg/openid/oauth2_test.go b/pkg/openid/oauth2_test.go
new file mode 100644
index 0000000..0b2e549
--- /dev/null
+++ b/pkg/openid/oauth2_test.go
@@ -0,0 +1,28 @@
+package openid
+
+import (
+	"net/url"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestStateMismatchError(t *testing.T) {
+	for _, tt := range []struct {
+		name, expected, actual string
+		assertion              assert.ErrorAssertionFunc
+	}{
+		{"missing actual state", "expected", "", assert.Error},
+		{"state mismatch", "match", "not-match", assert.Error},
+		{"state match", "match", "match", assert.NoError},
+	} {
+		t.Run(tt.name, func(t *testing.T) {
+			actual := url.Values{
+				"state": []string{tt.actual},
+			}
+
+			err := StateMismatchError(actual, tt.expected)
+			tt.assertion(t, err)
+		})
+	}
+}
diff --git a/pkg/openid/params.go b/pkg/openid/params.go
deleted file mode 100644
index d2db308..0000000
--- a/pkg/openid/params.go
+++ /dev/null
@@ -1,26 +0,0 @@
-package openid
-
-const (
-	ACRValues             = "acr_values"
-	ClientAssertion       = "client_assertion"
-	ClientAssertionType   = "client_assertion_type"
-	ClientID              = "client_id"
-	CodeChallenge         = "code_challenge"
-	CodeChallengeMethod   = "code_challenge_method"
-	Code                  = "code"
-	CodeVerifier          = "code_verifier"
-	Error                 = "error"
-	ErrorDescription      = "error_description"
-	GrantType             = "grant_type"
-	IDTokenHint           = "id_token_hint"
-	Nonce                 = "nonce"
-	PostLogoutRedirectURI = "post_logout_redirect_uri"
-	SessionState          = "session_state"
-	Sid                   = "sid"
-	State                 = "state"
-	RedirectURI           = "redirect_uri"
-	RefreshToken          = "refresh_token"
-	Resource              = "resource"
-	ResponseMode          = "response_mode"
-	UILocales             = "ui_locales"
-)
diff --git a/pkg/openid/params_values.go b/pkg/openid/params_values.go
deleted file mode 100644
index 5440ea6..0000000
--- a/pkg/openid/params_values.go
+++ /dev/null
@@ -1,6 +0,0 @@
-package openid
-
-const (
-	ClientAssertionTypeJwtBearer = "urn:ietf:params:oauth:client-assertion-type:jwt-bearer"
-	RefreshTokenValue            = "refresh_token"
-)
diff --git a/pkg/openid/response.go b/pkg/openid/response.go
deleted file mode 100644
index d78626c..0000000
--- a/pkg/openid/response.go
+++ /dev/null
@@ -1,17 +0,0 @@
-package openid
-
-// TokenResponse is the struct representing the HTTP response from OpenID Connect providers returning a token in
-// JSON form.
-type TokenResponse struct {
-	AccessToken  string `json:"access_token"`
-	ExpiresIn    int64  `json:"expires_in"`
-	RefreshToken string `json:"refresh_token"`
-	TokenType    string `json:"token_type"`
-}
-
-// TokenErrorResponse is the struct representing the HTTP error response returned from OpenID Connect providers
-// in JSON form.
-type TokenErrorResponse struct {
-	Error            string `json:"error"`
-	ErrorDescription string `json:"error_description"`
-}
diff --git a/pkg/session/id.go b/pkg/session/id.go
index b283941..08f03c5 100644
--- a/pkg/session/id.go
+++ b/pkg/session/id.go
@@ -43,9 +43,9 @@ func ExternalID(r *http.Request, cfg openidconfig.Provider, idToken *openid.IDTo
 func getSessionStateFrom(r *http.Request) (string, error) {
 	params := r.URL.Query()
 
-	sessionState := params.Get(openid.SessionState)
+	sessionState := params.Get("session_state")
 	if len(sessionState) == 0 {
-		return "", fmt.Errorf("missing required '%s' in params", openid.SessionState)
+		return "", fmt.Errorf("missing required 'session_state' in params")
 	}
 	return sessionState, nil
 }