Add generic oauth module

Signed-off-by: prichier <pascoualito@gmail.com>

oauth_generic.go

@@ -0,0 +1,114 @@
+package writefreely
+
+import (
+	"context"
+	"errors"
+	"net/http"
+	"net/url"
+	"strings"
+)
+
+type genericOauthClient struct {
+	ClientID         string
+	ClientSecret     string
+	AuthLocation     string
+	ExchangeLocation string
+	InspectLocation  string
+	CallbackLocation string
+	HttpClient       HttpClient
+}
+
+var _ oauthClient = genericOauthClient{}
+
+const (
+    genericOauthDisplayName = "oAuth"
+)
+
+func (c genericOauthClient) GetProvider() string {
+	return "generic"
+}
+
+func (c genericOauthClient) GetClientID() string {
+	return c.ClientID
+}
+
+func (c genericOauthClient) GetCallbackLocation() string {
+	return c.CallbackLocation
+}
+
+func (c genericOauthClient) buildLoginURL(state string) (string, error) {
+	u, err := url.Parse(c.AuthLocation)
+	if err != nil {
+		return "", err
+	}
+	q := u.Query()
+	q.Set("client_id", c.ClientID)
+	q.Set("redirect_uri", c.CallbackLocation)
+	q.Set("response_type", "code")
+	q.Set("state", state)
+	q.Set("scope", "read_user")
+	u.RawQuery = q.Encode()
+	return u.String(), nil
+}
+
+func (c genericOauthClient) exchangeOauthCode(ctx context.Context, code string) (*TokenResponse, error) {
+	form := url.Values{}
+	form.Add("grant_type", "authorization_code")
+	form.Add("redirect_uri", c.CallbackLocation)
+	form.Add("scope", "read_user")
+	form.Add("code", code)
+	req, err := http.NewRequest("POST", c.ExchangeLocation, strings.NewReader(form.Encode()))
+	if err != nil {
+		return nil, err
+	}
+	req.WithContext(ctx)
+	req.Header.Set("User-Agent", "writefreely")
+	req.Header.Set("Accept", "application/json")
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	req.SetBasicAuth(c.ClientID, c.ClientSecret)
+
+	resp, err := c.HttpClient.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	if resp.StatusCode != http.StatusOK {
+		return nil, errors.New("unable to exchange code for access token")
+	}
+
+	var tokenResponse TokenResponse
+	if err := limitedJsonUnmarshal(resp.Body, tokenRequestMaxLen, &tokenResponse); err != nil {
+		return nil, err
+	}
+	if tokenResponse.Error != "" {
+		return nil, errors.New(tokenResponse.Error)
+	}
+	return &tokenResponse, nil
+}
+
+func (c genericOauthClient) inspectOauthAccessToken(ctx context.Context, accessToken string) (*InspectResponse, error) {
+	req, err := http.NewRequest("GET", c.InspectLocation, nil)
+	if err != nil {
+		return nil, err
+	}
+	req.WithContext(ctx)
+	req.Header.Set("User-Agent", "writefreely")
+	req.Header.Set("Accept", "application/json")
+	req.Header.Set("Authorization", "Bearer "+accessToken)
+
+	resp, err := c.HttpClient.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	if resp.StatusCode != http.StatusOK {
+		return nil, errors.New("unable to inspect access token")
+	}
+
+	var inspectResponse InspectResponse
+	if err := limitedJsonUnmarshal(resp.Body, infoRequestMaxLen, &inspectResponse); err != nil {
+		return nil, err
+	}
+	if inspectResponse.Error != "" {
+		return nil, errors.New(inspectResponse.Error)
+	}
+	return &inspectResponse, nil
+}