chore: fix linter config and violations

Signed-off-by: Mark Sagi-Kazar <mark.sagikazar@gmail.com>

.golangci.yml

 run:
     timeout: 4m
-    skip-dirs:
-        - storage/ent/db # generated ent code
 
 linters-settings:
     depguard:
-      rules:
-        deprecated:
-          deny:
-            - pkg: "io/ioutil"
-              desc: "The 'io/ioutil' package is deprecated. Use corresponding 'os' or 'io' functions instead."
+        rules:
+            deprecated:
+                deny:
+                    - pkg: "io/ioutil"
+                      desc: "The 'io/ioutil' package is deprecated. Use corresponding 'os' or 'io' functions instead."
     gci:
-        local-prefixes: github.com/dexidp/dex
+        sections:
+            - standard
+            - default
+            - prefix(github.com/dexidp/dex)
     goimports:
         local-prefixes: github.com/dexidp/dex
 
-
 linters:
     disable-all: true
     enable:
         - depguard
         - dogsled
         - exhaustive
-        - exportloopref
         - gci
         - gochecknoinits
         - gocritic
@@ -92,3 +91,7 @@ linters:
         # - nestif
         # - testpackage
         # - wsl
+
+issues:
+    exclude-dirs:
+        - storage/ent/db # generated ent code

connector/saml/saml.go

@@ -467,7 +467,7 @@ func (p *provider) validateStatus(status *status) error {
 		if statusMessage != nil && statusMessage.Value != "" {
 			errorMessage += " -> " + statusMessage.Value
 		}
-		return fmt.Errorf(errorMessage)
+		return errors.New(errorMessage)
 	}
 	return nil
 }

server/introspectionhandler.go

@@ -170,7 +170,7 @@ func (s *Server) getTokenFromRequest(r *http.Request) (string, TokenTypeEnum, er
 		return "", 0, newIntrospectBadRequestError(fmt.Sprintf("HTTP method is \"%s\", expected \"POST\".", r.Method))
 	} else if err := r.ParseForm(); err != nil {
 		return "", 0, newIntrospectBadRequestError("Unable to parse HTTP body, make sure to send a properly formatted form request body.")
-	} else if r.PostForm == nil || len(r.PostForm) == 0 {
+	} else if len(r.PostForm) == 0 {
 		return "", 0, newIntrospectBadRequestError("The POST body can not be empty.")
 	} else if !r.PostForm.Has("token") {
 		return "", 0, newIntrospectBadRequestError("The POST body doesn't contain 'token' parameter.")