chore: do not use sentinel errors when unneeded

- main reason being it's a burden to always define sentinel errors at global scope, wrap them with `%w` instead of using a string directly
- only use sentinel errors when it has to be checked using `errors.Is`
- replace all usage of these sentinel errors in `fmt.Errorf` with direct strings that were in the sentinel error
- exclude the sentinel error definition requirement from .golangci.yml
- update unit tests to use ContainersError instead of ErrorIs so it stays as a "not a change detector test" without requiring a sentinel error

internal/server/middlewares/auth/lookup.go

@@ -21,7 +21,7 @@ func settingsToLookupMap(settings Settings) (routeToRoles map[string][]internalR
 		case AuthBasic:
 			checker = newBasicAuthMethod(role.Username, role.Password)
 		default:
-			return nil, fmt.Errorf("%w: %s", ErrMethodNotSupported, role.Auth)
+			return nil, fmt.Errorf("authentication method not supported: %s", role.Auth)
 		}
 
 		iRole := internalRole{

internal/server/middlewares/auth/lookup_test.go

@@ -13,7 +13,6 @@ func Test_settingsToLookupMap(t *testing.T) {
 	testCases := map[string]struct {
 		settings     Settings
 		routeToRoles map[string][]internalRole
-		errWrapped   error
 		errMessage   string
 	}{
 		"empty_settings": {
@@ -23,7 +22,6 @@ func Test_settingsToLookupMap(t *testing.T) {
 			settings: Settings{
 				Roles: []Role{{Name: "a", Auth: "bad"}},
 			},
-			errWrapped: ErrMethodNotSupported,
 			errMessage: "authentication method not supported: bad",
 		},
 		"success": {
@@ -51,9 +49,10 @@ func Test_settingsToLookupMap(t *testing.T) {
 			routeToRoles, err := settingsToLookupMap(testCase.settings)
 
 			assert.Equal(t, testCase.routeToRoles, routeToRoles)
-			assert.ErrorIs(t, err, testCase.errWrapped)
-			if testCase.errWrapped != nil {
+			if testCase.errMessage != "" {
 				assert.EqualError(t, err, testCase.errMessage)
+			} else {
+				assert.NoError(t, err)
 			}
 		})
 	}

internal/server/middlewares/auth/settings.go

@@ -3,7 +3,6 @@ package auth
 import (
 	"bytes"
 	"encoding/json"
-	"errors"
 	"fmt"
 	"net/http"
 	"slices"
@@ -106,28 +105,19 @@ type Role struct {
 	Routes []string `json:"-"`
 }
 
-var (
-	ErrMethodNotSupported      = errors.New("authentication method not supported")
-	ErrAPIKeyEmpty             = errors.New("api key is empty")
-	ErrBasicUsernameEmpty      = errors.New("username is empty")
-	ErrBasicPasswordEmpty      = errors.New("password is empty")
-	ErrRoutePathNotSupported   = errors.New("route path not supported by the control server")
-	ErrRouteMethodNotSupported = errors.New("route method not supported for the path")
-)
-
 func (r Role) Validate() (err error) {
 	err = validate.IsOneOf(r.Auth, AuthNone, AuthAPIKey, AuthBasic)
 	if err != nil {
-		return fmt.Errorf("%w: %s", ErrMethodNotSupported, r.Auth)
+		return fmt.Errorf("authentication method not supported: %s", r.Auth)
 	}
 
 	switch {
 	case r.Auth == AuthAPIKey && r.APIKey == "":
-		return fmt.Errorf("for role %s: %w", r.Name, ErrAPIKeyEmpty)
+		return fmt.Errorf("for role %s: api key is empty", r.Name)
 	case r.Auth == AuthBasic && r.Username == "":
-		return fmt.Errorf("for role %s: %w", r.Name, ErrBasicUsernameEmpty)
+		return fmt.Errorf("for role %s: username is empty", r.Name)
 	case r.Auth == AuthBasic && r.Password == "":
-		return fmt.Errorf("for role %s: %w", r.Name, ErrBasicPasswordEmpty)
+		return fmt.Errorf("for role %s: password is empty", r.Name)
 	}
 
 	for i, route := range r.Routes {
@@ -136,11 +126,11 @@ func (r Role) Validate() (err error) {
 		method, path := parts[0], parts[1]
 		methods, ok := validRoutes[path]
 		if !ok {
-			return fmt.Errorf("route %d of %d: %w: %s",
-				i+1, len(r.Routes), ErrRoutePathNotSupported, path)
+			return fmt.Errorf("route %d of %d: route path not supported by the control server: %s",
+				i+1, len(r.Routes), path)
 		} else if !slices.Contains(methods, method) {
-			return fmt.Errorf("route %d of %d: %w: %s for path %s",
-				i+1, len(r.Routes), ErrRouteMethodNotSupported, method, path)
+			return fmt.Errorf("route %d of %d: route method not supported for the path: %s for path %s",
+				i+1, len(r.Routes), method, path)
 		}
 	}