Add many error checks around authorization

pkg/indieauth/auth.go

@@ -9,6 +9,7 @@ import (
 	"net"
 	"net/http"
 	"net/url"
+	"strings"
 
 	"linkheader"
 
@@ -28,6 +29,8 @@ type TokenResponse struct {
 	AccessToken      string `json:"access_token"`
 	TokenType        string `json:"token_type"`
 	Scope            string `json:"scope"`
+	Error            string `json:"error"`
+	ErrorDescription string `json:"error_description"`
 }
 
 func GetEndpoints(me *url.URL) (Endpoints, error) {
@@ -151,17 +154,52 @@ func Authorize(me *url.URL, endpoints Endpoints, clientID, scope string) (TokenR
 	reqValues.Add("client_id", clientID)
 	reqValues.Add("me", me.String())
 
-	res, err := http.PostForm(endpoints.TokenEndpoint, reqValues)
+	req, err := http.NewRequest(http.MethodPost, endpoints.TokenEndpoint, strings.NewReader(reqValues.Encode()))
 	if err != nil {
 		return tokenResponse, err
 	}
+	req.Header.Add("Content-Type", "application/x-www-form-urlencoded")
+	req.Header.Add("Accept", "application/json")
 
+	res, err := http.DefaultClient.Do(req)
+	if err != nil {
+		return tokenResponse, err
+	}
 	defer res.Body.Close()
 
+	if res.StatusCode != 200 {
+		return TokenResponse{}, fmt.Errorf("status code %d, instead of 200", res.StatusCode)
+	}
+
+	if strings.HasPrefix(res.Header.Get("content-type"), "application/json") {
 		dec := json.NewDecoder(res.Body)
 		err = dec.Decode(&tokenResponse)
 		if err != nil {
-		return tokenResponse, err
+			return tokenResponse, fmt.Errorf("error while parsing response body with content-type %s as json: %s", res.Header.Get("content-type"), err)
+		}
+		if tokenResponse.Me == "" && tokenResponse.Error != "" {
+			return tokenResponse, fmt.Errorf("received error from endpoint: %s, %s", tokenResponse.Error, tokenResponse.ErrorDescription)
+		}
+	} else if strings.HasPrefix(res.Header.Get("content-type"), "application/x-www-form-urlencoded") {
+		body, err := ioutil.ReadAll(res.Body)
+		if err != nil {
+			return tokenResponse, fmt.Errorf("error while reading response body with content-type %s: %s", res.Header.Get("content-type"), err)
+		}
+
+		values, err := url.ParseQuery(string(body))
+		if err != nil {
+			return tokenResponse, fmt.Errorf("error while parsing response body with content-type %s as application/x-www-form-urlencoded: %s\nbody was: %q\n", res.Header.Get("content-type"), err, body)
+		}
+
+		if values.Get("me") == "" {
+			if errTxt := values.Get("error"); errTxt != "" {
+				return tokenResponse, fmt.Errorf("received error from endpoint: %s, %s", errTxt, values.Get("error_description"))
+			}
+		}
+		tokenResponse.Me = values.Get("me")
+		tokenResponse.AccessToken = values.Get("token")
+		tokenResponse.TokenType = values.Get("token_type")
+		tokenResponse.Scope = values.Get("scope")
 	}
 
 	return tokenResponse, nil