diff --git a/app_user_test.go b/app_user_test.go
index 3623d08..d060727 100644
--- a/app_user_test.go
+++ b/app_user_test.go
@@ -366,8 +366,7 @@ func TestCreateUser(t *testing.T) {
 		_, err = psg.CreateUser(createUserBody)
 
 		require.NotNil(t, err)
-		expectedErrorText := "email: cannot be blank; phone: cannot be blank."
-		badRequestAsserts(t, err, expectedErrorText)
+		assert.Equal(t, "At least one of args.Email or args.Phone is required.", err.Error())
 	})
 
 	t.Run("Error: unauthorized", func(t *testing.T) {
diff --git a/auth.go b/auth.go
index 4fa1def..69674cd 100644
--- a/auth.go
+++ b/auth.go
@@ -6,6 +6,7 @@ import (
 	"fmt"
 
 	"github.com/golang-jwt/jwt"
+	gojwt "github.com/golang-jwt/jwt"
 	"github.com/lestrrat-go/jwx/v2/jwk"
 )
 
@@ -38,8 +39,8 @@ func newAuth(appID string, client *ClientWithResponses) (*auth, error) {
 }
 
 // CreateMagicLink creates a Magic Link for your app.
-func (a *auth) CreateMagicLink(createMagicLinkBody CreateMagicLinkBody) (*MagicLink, error) {
-	res, err := a.client.CreateMagicLinkWithResponse(context.Background(), a.appID, createMagicLinkBody)
+func (a *auth) CreateMagicLink(args CreateMagicLinkBody) (*MagicLink, error) {
+	res, err := a.client.CreateMagicLinkWithResponse(context.Background(), a.appID, args)
 	if err != nil {
 		return nil, err
 	}
@@ -52,13 +53,17 @@ func (a *auth) CreateMagicLink(createMagicLinkBody CreateMagicLinkBody) (*MagicL
 }
 
 // ValidateJWT validates the JWT and returns the user ID.
-func (a *auth) ValidateJWT(authToken string) (string, error) {
-	parsedToken, err := jwt.Parse(authToken, a.getPublicKey)
+func (a *auth) ValidateJWT(jwt string) (string, error) {
+	if jwt == "" {
+		return "", errors.New("jwt is required.")
+	}
+
+	parsedToken, err := gojwt.Parse(jwt, a.getPublicKey)
 	if err != nil {
 		return "", err
 	}
 
-	claims, ok := parsedToken.Claims.(jwt.MapClaims)
+	claims, ok := parsedToken.Claims.(gojwt.MapClaims)
 	if !ok {
 		return "", errors.New("failed to extract claims from JWT")
 	}
diff --git a/authentication.go b/authentication.go
index d1638cd..b32d03a 100644
--- a/authentication.go
+++ b/authentication.go
@@ -55,6 +55,10 @@ func (a *App) AuthenticateRequestWithCookie(r *http.Request) (string, error) {
 //
 // Deprecated: use `Passage.Auth.ValidateJWT` instead.
 func (a *App) ValidateAuthToken(authToken string) (string, bool) {
+	if authToken == "" {
+		return "", false
+	}
+
 	parsedToken, err := jwt.Parse(authToken, a.Auth.getPublicKey)
 	if err != nil {
 		return "", false
diff --git a/user.go b/user.go
index 05f1afa..8d79cd2 100644
--- a/user.go
+++ b/user.go
@@ -2,6 +2,7 @@ package passage
 
 import (
 	"context"
+	"errors"
 	"net/http"
 	"strings"
 )
@@ -24,6 +25,10 @@ func newUser(appID string, client *ClientWithResponses) *user {
 
 // Get retrieves a user's object using their user ID.
 func (u *user) Get(userID string) (*PassageUser, error) {
+	if userID == "" {
+		return nil, errors.New("userID is required.")
+	}
+
 	res, err := u.client.GetUserWithResponse(context.Background(), u.appID, userID)
 	if err != nil {
 		return nil, err
@@ -38,6 +43,10 @@ func (u *user) Get(userID string) (*PassageUser, error) {
 
 // GetByIdentifier retrieves a user's object using their user identifier.
 func (u *user) GetByIdentifier(identifier string) (*PassageUser, error) {
+	if identifier == "" {
+		return nil, errors.New("identifier is required.")
+	}
+
 	limit := 1
 	lowerIdentifier := strings.ToLower(identifier)
 	res, err := u.client.ListPaginatedUsersWithResponse(
@@ -72,6 +81,10 @@ func (u *user) GetByIdentifier(identifier string) (*PassageUser, error) {
 
 // Activate activates a user using their user ID.
 func (u *user) Activate(userID string) (*PassageUser, error) {
+	if userID == "" {
+		return nil, errors.New("userID is required.")
+	}
+
 	res, err := u.client.ActivateUserWithResponse(context.Background(), u.appID, userID)
 	if err != nil {
 		return nil, err
@@ -86,6 +99,10 @@ func (u *user) Activate(userID string) (*PassageUser, error) {
 
 // Deactivate deactivates a user using their user ID.
 func (u *user) Deactivate(userID string) (*PassageUser, error) {
+	if userID == "" {
+		return nil, errors.New("userID is required.")
+	}
+
 	res, err := u.client.DeactivateUserWithResponse(context.Background(), u.appID, userID)
 	if err != nil {
 		return nil, err
@@ -100,6 +117,10 @@ func (u *user) Deactivate(userID string) (*PassageUser, error) {
 
 // Update updates a user.
 func (u *user) Update(userID string, options UpdateUserOptions) (*PassageUser, error) {
+	if userID == "" {
+		return nil, errors.New("userID is required.")
+	}
+
 	res, err := u.client.UpdateUserWithResponse(context.Background(), u.appID, userID, options)
 	if err != nil {
 		return nil, err
@@ -114,6 +135,10 @@ func (u *user) Update(userID string, options UpdateUserOptions) (*PassageUser, e
 
 // Create creates a user.
 func (u *user) Create(args CreateUserArgs) (*PassageUser, error) {
+	if args.Email == "" && args.Phone == "" {
+		return nil, errors.New("At least one of args.Email or args.Phone is required.")
+	}
+
 	res, err := u.client.CreateUserWithResponse(context.Background(), u.appID, args)
 	if err != nil {
 		return nil, err
@@ -128,6 +153,10 @@ func (u *user) Create(args CreateUserArgs) (*PassageUser, error) {
 
 // Delete deletes a user using their user ID.
 func (u *user) Delete(userID string) error {
+	if userID == "" {
+		return errors.New("userID is required.")
+	}
+
 	res, err := u.client.DeleteUserWithResponse(context.Background(), u.appID, userID)
 	if err != nil {
 		return err
@@ -142,6 +171,10 @@ func (u *user) Delete(userID string) error {
 
 // ListDevices retrieves a user's webauthn devices using their user ID.
 func (u *user) ListDevices(userID string) ([]WebAuthnDevices, error) {
+	if userID == "" {
+		return nil, errors.New("userID is required.")
+	}
+
 	res, err := u.client.ListUserDevicesWithResponse(context.Background(), u.appID, userID)
 	if err != nil {
 		return nil, err
@@ -156,6 +189,14 @@ func (u *user) ListDevices(userID string) ([]WebAuthnDevices, error) {
 
 // RevokeDevice revokes user's webauthn device using their user ID and the device ID.
 func (u *user) RevokeDevice(userID string, deviceID string) error {
+	if userID == "" {
+		return errors.New("userID is required.")
+	}
+
+	if deviceID == "" {
+		return errors.New("deviceID is required.")
+	}
+
 	res, err := u.client.DeleteUserDevicesWithResponse(context.Background(), u.appID, userID, deviceID)
 	if err != nil {
 		return err
@@ -170,6 +211,10 @@ func (u *user) RevokeDevice(userID string, deviceID string) error {
 
 // RevokeRefreshTokens revokes all of a user's Refresh Tokens using their User ID.
 func (u *user) RevokeRefreshTokens(userID string) error {
+	if userID == "" {
+		return errors.New("userID is required.")
+	}
+
 	res, err := u.client.RevokeUserRefreshTokensWithResponse(context.Background(), u.appID, userID)
 	if err != nil {
 		return err
diff --git a/user_test.go b/user_test.go
index 33a59da..6636266 100644
--- a/user_test.go
+++ b/user_test.go
@@ -367,8 +367,7 @@ func TestCreate(t *testing.T) {
 		_, err = psg.User.Create(createUserBody)
 
 		require.NotNil(t, err)
-		expectedMessage := "email: cannot be blank; phone: cannot be blank."
-		passageBadRequestAsserts(t, err, expectedMessage)
+		assert.Equal(t, "At least one of args.Email or args.Phone is required.", err.Error())
 	})
 
 	t.Run("Error: unauthorized", func(t *testing.T) {