fix: unmarshalling of scopes in access token (#327)

The Scopes field in accessTokenClaims should be a  SpaceDelimitedArray,
in order to allow for correct unmarshalling.

Fixes #318

* adjust test data

pkg/oidc/regression_data/oidc.AccessTokenClaims.json

@@ -13,10 +13,7 @@
 		"some",
 		"methods"
 	],
-	"scope": [
-		"email",
-		"phone"
-	],
+	"scope": "email phone",
 	"client_id": "777",
 	"exp": 12345,
 	"iat": 12000,

pkg/oidc/token.go

@@ -97,7 +97,7 @@ func (c *TokenClaims) SetSignatureAlgorithm(algorithm jose.SignatureAlgorithm) {
 
 type AccessTokenClaims struct {
 	TokenClaims
-	Scopes []string       `json:"scope,omitempty"`
+	Scopes SpaceDelimitedArray `json:"scope,omitempty"`
 	Claims map[string]any      `json:"-"`
 }