Correct client behaviours for option handling

A config file is not required - don't error if one doesn't exist.

Don't overwrite default options with an empty string.

client/config.go

 package client
 
 import (
+	"os"
+
 	"github.com/mitchellh/go-homedir"
 	"github.com/spf13/pflag"
 	"github.com/spf13/viper"
@@ -28,11 +30,13 @@ func setDefaults() {
 // ReadConfig reads the client configuration from a file into a Config struct.
 func ReadConfig(path string) (*Config, error) {
 	setDefaults()
+	if _, err := os.Stat(path); err == nil {
 		viper.SetConfigFile(path)
 		viper.SetConfigType("hcl")
 		if err := viper.ReadInConfig(); err != nil {
 			return nil, err
 		}
+	}
 	c := &Config{}
 	if err := viper.Unmarshal(c); err != nil {
 		return nil, err

client/keys.go

@@ -59,9 +59,11 @@ func pemBlockForKey(priv interface{}) (*pem.Block, error) {
 // Default is "rsa"
 func KeyType(keyType string) KeyOption {
 	return func(o *options) {
+		if keyType != "" {
 			o.keytype = keyType
 		}
 	}
+}
 
 // KeySize sets the size of the key in bits.
 // RSA keys must be a minimum of 1024 bits. The default is 2048 bits.

cmd/cashier/main.go

@@ -36,17 +36,17 @@ func main() {
 
 	c, err := client.ReadConfig(*cfg)
 	if err != nil {
-		log.Printf("Error parsing config file: %v\n", err)
-	}
-	fmt.Printf("Your browser has been opened to visit %s\n", c.CA)
-	if err := browser.OpenURL(c.CA); err != nil {
-		fmt.Println("Error launching web browser. Go to the link in your web browser")
+		log.Printf("Configuration error: %v\n", err)
 	}
 	fmt.Println("Generating new key pair")
 	priv, pub, err := client.GenerateKey(client.KeyType(c.Keytype), client.KeySize(c.Keysize))
 	if err != nil {
 		log.Fatalln("Error generating key pair: ", err)
 	}
+	fmt.Printf("Your browser has been opened to visit %s\n", c.CA)
+	if err := browser.OpenURL(c.CA); err != nil {
+		fmt.Println("Error launching web browser. Go to the link in your web browser")
+	}
 
 	fmt.Print("Enter token: ")
 	var token string