Add support to migrate from gogs (#14342)

Add support to migrate gogs:

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Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Andrew Thornton <art27@cantab.net>

vendor/github.com/gogs/go-gogs-client/user_app.go

@@ -0,0 +1,46 @@
+// Copyright 2014 The Gogs Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package gogs
+
+import (
+	"bytes"
+	"encoding/base64"
+	"encoding/json"
+	"fmt"
+	"net/http"
+)
+
+func BasicAuthEncode(user, pass string) string {
+	return base64.StdEncoding.EncodeToString([]byte(user + ":" + pass))
+}
+
+// AccessToken represents a API access token.
+type AccessToken struct {
+	Name string `json:"name"`
+	Sha1 string `json:"sha1"`
+}
+
+func (c *Client) ListAccessTokens(user, pass string) ([]*AccessToken, error) {
+	tokens := make([]*AccessToken, 0, 10)
+	return tokens, c.getParsedResponse("GET", fmt.Sprintf("/users/%s/tokens", user),
+		http.Header{"Authorization": []string{"Basic " + BasicAuthEncode(user, pass)}}, nil, &tokens)
+}
+
+type CreateAccessTokenOption struct {
+	Name string `json:"name" binding:"Required"`
+}
+
+func (c *Client) CreateAccessToken(user, pass string, opt CreateAccessTokenOption) (*AccessToken, error) {
+	body, err := json.Marshal(&opt)
+	if err != nil {
+		return nil, err
+	}
+	t := new(AccessToken)
+	return t, c.getParsedResponse("POST", fmt.Sprintf("/users/%s/tokens", user),
+		http.Header{
+			"content-type":  []string{"application/json"},
+			"Authorization": []string{"Basic " + BasicAuthEncode(user, pass)}},
+		bytes.NewReader(body), t)
+}