added oauth flow to get authorization code

internal/discord/oauth.go

@@ -0,0 +1,39 @@
+package discord
+
+import (
+	"fmt"
+	"net/url"
+
+	"github.com/pkg/errors"
+)
+
+type Token struct {
+	AccessToken  string
+	TokenType    string
+	ExpiresIn    int
+	RefreshToken string
+	Scope        string
+}
+
+const oauthurl string = "https://discord.com/oauth2/authorize"
+
+func GetOAuthLink(cfg *Config, state string, trustedHost string) (string, error) {
+	if cfg == nil {
+		return "", errors.New("cfg cannot be nil")
+	}
+	if state == "" {
+		return "", errors.New("state cannot be empty")
+	}
+	if trustedHost == "" {
+		return "", errors.New("trustedHost cannot be empty")
+	}
+	values := url.Values{}
+	values.Add("response_type", "code")
+	values.Add("client_id", cfg.ClientID)
+	values.Add("scope", cfg.OAuthScopes)
+	values.Add("state", state)
+	values.Add("redirect_uri", fmt.Sprintf("%s/%s", trustedHost, cfg.RedirectPath))
+	values.Add("prompt", "none")
+
+	return fmt.Sprintf("%s?%s", oauthurl, values.Encode()), nil
+}