load cert from file rather than embed

.gitignore

@@ -1 +1,2 @@
-log.txt
+log.txt
+*.pem

main.go

@@ -3,8 +3,12 @@ package main
 import (
 	"crypto/x509"
 	"encoding/json"
+	"encoding/pem"
 	"flag"
 	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
 
 	auth "github.com/korylprince/go-ad-auth/v3"
 )
@@ -71,6 +75,37 @@ lS3ZUQcHCLtUbTw=
 -----END CERTIFICATE-----
 `
 
+func GetFilePath(path string) string {
+	// Check for empty filename
+	if len(path) == 0 {
+		return ""
+	}
+
+	// check if filename exists
+	if _, err := os.Stat(path); os.IsNotExist((err)) {
+		fmt.Printf("File '%s' not found, searching in same directory as binary\n", path)
+		// if not, check that it exists in the same directory as the currently executing binary
+		ex, err2 := os.Executable()
+		if err2 != nil {
+			//log.Printf("Error determining binary path : '%s'", err)
+			return ""
+		}
+		binaryPath := filepath.Dir(ex)
+		path = filepath.Join(binaryPath, path)
+	}
+	return path
+}
+
+func isFlagPassed(name string) bool {
+	found := false
+	flag.Visit(func(f *flag.Flag) {
+		if f.Name == name {
+			found = true
+		}
+	})
+	return found
+}
+
 func main() {
 	var output Output
 
@@ -79,6 +114,7 @@ func main() {
 	baseDN := flag.String("baseDN", "OU=Users,DC=example,DC=com", "Base DN to use when attempting to bind to AD")
 	username := flag.String("username", "user", "Username to use when attempting to bind to AD")
 	password := flag.String("password", "pass", "Password to use when attempting to bind to AD")
+	certFile := flag.String("cert-file", "rootca.pem", "Filename to load trusted certificate from")
 	flag.Parse()
 
 	output.Server = *server
@@ -93,14 +129,42 @@ func main() {
 		return
 	}
 
-	// Add custom certificate to the system cert pool
-	ok := system.AppendCertsFromPEM([]byte(WSDCCertPem))
-	if !ok {
-		output.AuthSuccess = false
-		output.Error = "failed to parse WSDC intermediate certificate"
-		b, _ := json.Marshal(output)
-		fmt.Println(string(b))
-		return
+	// only try to load certificate from file if the command line argument was specified
+	if isFlagPassed("cert-file") {
+		// Try to read the file
+		cf, err := ioutil.ReadFile(GetFilePath(*certFile))
+		if err != nil {
+			output.AuthSuccess = false
+			output.Error = err.Error()
+			b, _ := json.Marshal(output)
+			fmt.Println(string(b))
+			return
+		}
+
+		// Get the certificate from the file
+		cpb, _ := pem.Decode(cf)
+		crt, err := x509.ParseCertificate(cpb.Bytes)
+
+		if err != nil {
+			output.AuthSuccess = false
+			output.Error = err.Error()
+			b, _ := json.Marshal(output)
+			fmt.Println(string(b))
+			return
+		}
+
+		// Add custom certificate to the system cert pool
+		system.AddCert(crt)
+		/*
+			ok := system.AppendCertsFromPEM(crt)
+			if !ok {
+				output.AuthSuccess = false
+				output.Error = "failed to parse WSDC intermediate certificate"
+				b, _ := json.Marshal(output)
+				fmt.Println(string(b))
+				return
+			}
+		*/
 	}
 
 	config := &auth.Config{