[#2533] added VK OAuth2 provider

Co-authored-by: Valentine <xb2w1z@gmail.com>

tools/auth/vk.go

@@ -0,0 +1,85 @@
+package auth
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"strconv"
+	"strings"
+
+	"golang.org/x/oauth2"
+	"golang.org/x/oauth2/vk"
+)
+
+var _ Provider = (*VK)(nil)
+
+// NameVK is the unique name of the VK provider.
+const NameVK string = "vk"
+
+// VK allows authentication via VK OAuth2.
+type VK struct {
+	*baseProvider
+}
+
+// NewVKProvider creates new VK provider instance with some defaults.
+//
+// Docs: https://dev.vk.com/api/oauth-parameters
+func NewVKProvider() *VK {
+	return &VK{&baseProvider{
+		ctx:        context.Background(),
+		scopes:     []string{"email"},
+		authUrl:    vk.Endpoint.AuthURL,
+		tokenUrl:   vk.Endpoint.TokenURL,
+		userApiUrl: "https://api.vk.com/method/users.get?fields=photo_max,screen_name&v=5.131",
+	}}
+}
+
+// FetchAuthUser returns an AuthUser instance based on VK's user api.
+//
+// API reference: https://dev.vk.com/method/users.get
+func (p *VK) FetchAuthUser(token *oauth2.Token) (*AuthUser, error) {
+	data, err := p.FetchRawUserData(token)
+	if err != nil {
+		return nil, err
+	}
+
+	rawUser := map[string]any{}
+	if err := json.Unmarshal(data, &rawUser); err != nil {
+		return nil, err
+	}
+
+	extracted := struct {
+		Response []struct {
+			Id        int    `json:"id"`
+			FirstName string `json:"first_name"`
+			LastName  string `json:"last_name"`
+			Username  string `json:"screen_name"`
+			AvatarUrl string `json:"photo_max"`
+		} `json:"response"`
+	}{}
+
+	if err := json.Unmarshal(data, &extracted); err != nil {
+		return nil, err
+	}
+
+	if len(extracted.Response) == 0 {
+		return nil, errors.New("missing response entry")
+	}
+
+	user := &AuthUser{
+		Id:           strconv.Itoa(extracted.Response[0].Id),
+		Name:         strings.TrimSpace(extracted.Response[0].FirstName + " " + extracted.Response[0].LastName),
+		Username:     extracted.Response[0].Username,
+		AvatarUrl:    extracted.Response[0].AvatarUrl,
+		RawUser:      rawUser,
+		AccessToken:  token.AccessToken,
+		RefreshToken: token.RefreshToken,
+	}
+
+	if email := token.Extra("email"); email != nil {
+		user.Email = fmt.Sprint(email)
+	}
+
+	return user, nil
+}