refactor: remove oauth2.include_legacy_error_fields config

BREAKING CHANGE: OAuth2 errors can no longer be returned in the legacy error format. Essentially, fields `error_hint`, `error_debug` have been removed. Option `oauth2.include_legacy_error_fields` has been removed.

driver/config/provider.go

@@ -71,7 +71,6 @@ const (
 	KeyCGroupsV1AutoMaxProcsEnabled              = "cgroups.v1.auto_max_procs_enabled"
 	KeyGrantAllClientCredentialsScopesPerDefault = "oauth2.client_credentials.default_grant_allowed_scope" // #nosec G101
 	KeyExposeOAuth2Debug                         = "oauth2.expose_internal_errors"
-	KeyOAuth2LegacyErrors                        = "oauth2.include_legacy_error_fields"
 	KeyExcludeNotBeforeClaim                     = "oauth2.exclude_not_before_claim"
 	KeyAllowedTopLevelClaims                     = "oauth2.allowed_top_level_claims"
 	KeyOAuth2GrantJWTIDOptional                  = "oauth2.grant.jwt.jti_optional"
@@ -387,10 +386,6 @@ func (p *DefaultProvider) GetSendDebugMessagesToClients(ctx context.Context) boo
 	return p.getProvider(ctx).Bool(KeyExposeOAuth2Debug)
 }
 
-func (p *DefaultProvider) GetUseLegacyErrorFormat(ctx context.Context) bool {
-	return p.getProvider(ctx).Bool(KeyOAuth2LegacyErrors)
-}
-
 func (p *DefaultProvider) GetEnforcePKCE(ctx context.Context) bool {
 	return p.getProvider(ctx).Bool(KeyPKCEEnforced)
 }

oauth2/handler.go

@@ -792,7 +792,7 @@ func (h *Handler) writeAuthorizeError(w http.ResponseWriter, r *http.Request, ar
 }
 
 func (h *Handler) forwardError(w http.ResponseWriter, r *http.Request, err error) {
-	rfcErr := fosite.ErrorToRFC6749Error(err).WithLegacyFormat(h.c.GetUseLegacyErrorFormat(r.Context())).WithExposeDebug(h.c.GetSendDebugMessagesToClients(r.Context()))
+	rfcErr := fosite.ErrorToRFC6749Error(err).WithExposeDebug(h.c.GetSendDebugMessagesToClients(r.Context()))
 	query := rfcErr.ToValues()
 	http.Redirect(w, r, urlx.CopyWithQuery(h.c.ErrorURL(r.Context()), query).String(), http.StatusFound)
 }

spec/config.json

@@ -761,12 +761,6 @@
             }
           }
         },
-        "include_legacy_error_fields": {
-          "type": "boolean",
-          "description": "Set this to true if you want to include the `error_hint` and `error_debug` legacy fields in error responses. We recommend to set this to `false` unless you have clients using these fields.",
-          "default": false,
-          "examples": [true]
-        },
         "exclude_not_before_claim": {
           "type": "boolean",
           "description": "Set to true if you want to exclude claim `nbf (not before)` part of access token.",