fix: unmarshal is_private_email correctly (#1402)

## What kind of change does this PR introduce?
* Apple returns either a boolean or string value in `is_private_email`
which is why we need to implement our own custom unmarshaler to deal
with it
(https://developer.apple.com/documentation/sign_in_with_apple/sign_in_with_apple_rest_api/authenticating_users_with_sign_in_with_apple)

internal/api/provider/apple.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding/json"
 	"net/url"
+	"strconv"
 	"strings"
 
 	"github.com/coreos/go-oidc/v3/oidc"
@@ -17,10 +18,36 @@ const IssuerApple = "https://appleid.apple.com"
 // AppleProvider stores the custom config for apple provider
 type AppleProvider struct {
 	*oauth2.Config
-
 	oidc *oidc.Provider
 }
 
+type IsPrivateEmail bool
+
+// Apple returns an is_private_email field that could be a string or boolean value so we need to implement a custom unmarshaler
+// https://developer.apple.com/documentation/sign_in_with_apple/sign_in_with_apple_rest_api/authenticating_users_with_sign_in_with_apple
+func (b *IsPrivateEmail) UnmarshalJSON(data []byte) error {
+	var boolVal bool
+	if err := json.Unmarshal(data, &boolVal); err == nil {
+		*b = IsPrivateEmail(boolVal)
+		return nil
+	}
+
+	// ignore the error and try to unmarshal as a string
+	var strVal string
+	if err := json.Unmarshal(data, &strVal); err != nil {
+		return err
+	}
+
+	var err error
+	boolVal, err = strconv.ParseBool(strVal)
+	if err != nil {
+		return err
+	}
+
+	*b = IsPrivateEmail(boolVal)
+	return nil
+}
+
 type appleName struct {
 	FirstName string `json:"firstName"`
 	LastName  string `json:"lastName"`

internal/api/provider/oidc.go

@@ -122,8 +122,8 @@ type AppleIDTokenClaims struct {
 
 	Email string `json:"email"`
 
-	AuthTime       *float64 `json:"auth_time"`
-	IsPrivateEmail *bool    `json:"is_private_email,string"`
+	AuthTime       *float64        `json:"auth_time"`
+	IsPrivateEmail *IsPrivateEmail `json:"is_private_email"`
 }
 
 func parseAppleIDToken(token *oidc.IDToken) (*oidc.IDToken, *UserProvidedData, error) {