[#33] added Twitter OAuth2 provider

tools/auth/auth.go

@@ -92,6 +92,8 @@ func NewProviderByName(name string) (Provider, error) {
 		return NewGitlabProvider(), nil
 	case NameDiscord:
 		return NewDiscordProvider(), nil
+	case NameTwitter:
+		return NewTwitterProvider(), nil
 	default:
 		return nil, errors.New("Missing provider " + name)
 	}

tools/auth/twitter.go

@@ -0,0 +1,60 @@
+package auth
+
+import (
+	"golang.org/x/oauth2"
+)
+
+var _ Provider = (*Twitter)(nil)
+
+// NameTwitter is the unique name of the Twitter provider.
+const NameTwitter string = "twitter"
+
+// Twitter allows authentication via Twitter OAuth2.
+type Twitter struct {
+	*baseProvider
+}
+
+// NewTwitterProvider creates new Twitter provider instance with some defaults.
+func NewTwitterProvider() *Twitter {
+	return &Twitter{&baseProvider{
+		scopes: []string{
+			"users.read",
+
+			// we don't actually use this scope, but for some reason it is required by the `/2/users/me` endpoint
+			// (see https://developer.twitter.com/en/docs/twitter-api/users/lookup/api-reference/get-users-me)
+			"tweet.read",
+		},
+		authUrl:    "https://twitter.com/i/oauth2/authorize",
+		tokenUrl:   "https://api.twitter.com/2/oauth2/token",
+		userApiUrl: "https://api.twitter.com/2/users/me?user.fields=id,name,profile_image_url",
+	}}
+}
+
+// FetchAuthUser returns an AuthUser instance based on the Twitter's user api.
+func (p *Twitter) FetchAuthUser(token *oauth2.Token) (*AuthUser, error) {
+	// https://developer.twitter.com/en/docs/twitter-api/users/lookup/api-reference/get-users-me
+	rawData := struct {
+		Data struct {
+			Id              string `json:"id"`
+			Name            string `json:"name"`
+			ProfileImageUrl string `json:"profile_image_url"`
+
+			// NB! At the time of writing, Twitter OAuth2 doesn't support returning the user email address
+			// (see https://twittercommunity.com/t/which-api-to-get-user-after-oauth2-authorization/162417/33)
+			Email string `json:"email"`
+		} `json:"data"`
+	}{}
+
+	if err := p.FetchRawUserData(token, &rawData); err != nil {
+		return nil, err
+	}
+
+	user := &AuthUser{
+		Id:        rawData.Data.Id,
+		Name:      rawData.Data.Name,
+		Email:     rawData.Data.Email,
+		AvatarUrl: rawData.Data.ProfileImageUrl,
+	}
+
+	return user, nil
+}