short-d/short

package google

import (
    "net/http"
    "net/url"
    "strings"

    "github.com/short-d/app/fw/webreq"
    "github.com/short-d/short/backend/app/usecase/sso"
)

const (
    authorizationAPI = "https://accounts.google.com/o/oauth2/v2/auth"
    accessTokenAPI   = "https://www.googleapis.com/oauth2/v4/token"
)

var _ sso.IdentityProvider = (*IdentityProvider)(nil)

type scope = string

const (
    email   = "email"
    profile = "profile"
)

// IdentityProvider represents Google OAuth service.
type IdentityProvider struct {
    clientID     string
    clientSecret string
    httpRequest  webreq.HTTP
    redirectURI  string
}

// GetAuthorizationURL retrieves the URL of Google sign in page.
func (g IdentityProvider) GetAuthorizationURL() string {
    clientID := g.clientID
    redirectURI := g.redirectURI

    u, err := url.Parse(authorizationAPI)
    if err != nil {
        return ""
    }

    scopes := []scope{email, profile}

    query := u.Query()
    query.Set("client_id", clientID)
    query.Set("redirect_uri", redirectURI)
    query.Set("scope", strings.Join(scopes, " "))
    query.Set("include_granted_scopes", "true")
    query.Set("response_type", "code")
    u.RawQuery = query.Encode()

    return u.String()
}

// RequestAccessToken retrieves access token of user's Google account using
// authorization code.
func (g IdentityProvider) RequestAccessToken(authorizationCode string) (string, error) {
    grantType := "authorization_code"
    clientID := g.clientID
    clientSecret := g.clientSecret
    redirectURI := g.redirectURI

    u, err := url.Parse(accessTokenAPI)
    if err != nil {
        return "", err
    }

    query := url.Values{}
    query.Set("code", authorizationCode)
    query.Set("client_id", clientID)
    query.Set("client_secret", clientSecret)
    query.Set("redirect_uri", redirectURI)
    query.Set("grant_type", grantType)
    u.RawQuery = query.Encode()

    apiRes := accessTokenResponse{}
    err = g.httpRequest.JSON(http.MethodPost, u.String(), map[string]string{}, "", &apiRes)
    if err != nil {
        return "", err
    }

    return apiRes.AccessToken, nil
}

type accessTokenResponse struct {
    AccessToken string `json:"access_token"`
    TokenType   string `json:"token_type"`
}

// NewIdentityProvider initializes Google OAuth service.
func NewIdentityProvider(http webreq.HTTP, clientID string, clientSecret string, redirectURI string) IdentityProvider {
    return IdentityProvider{
        clientID:     clientID,
        clientSecret: clientSecret,
        httpRequest:  http,
        redirectURI:  redirectURI,
    }
}