diff --git a/oauth_generic.go b/oauth_generic.go
index ba8b97e..ccf6a0f 100644
--- a/oauth_generic.go
+++ b/oauth_generic.go
@@ -1,126 +1,142 @@
+/*
+ * Copyright © 2020-2021 A Bunch Tell LLC and respective authors.
+ *
+ * This file is part of WriteFreely.
+ *
+ * WriteFreely is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License, included
+ * in the LICENSE file in this source code package.
+ */
+
 package writefreely
 
 import (
 	"context"
 	"errors"
+	"fmt"
+	"github.com/writeas/web-core/log"
 	"net/http"
 	"net/url"
 	"strings"
 )
 
 type genericOauthClient struct {
 	ClientID         string
 	ClientSecret     string
 	AuthLocation     string
 	ExchangeLocation string
 	InspectLocation  string
 	CallbackLocation string
 	Scope            string
 	MapUserID        string
 	MapUsername      string
 	MapDisplayName   string
 	MapEmail         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", c.Scope)
 	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", c.Scope)
 	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", ServerUserAgent(""))
 	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", ServerUserAgent(""))
 	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")
 	}
 
 	// since we don't know what the JSON from the server will look like, we create a
 	// generic interface and then map manually to values set in the config
 	var genericInterface map[string]interface{}
 	if err := limitedJsonUnmarshal(resp.Body, infoRequestMaxLen, &genericInterface); err != nil {
 		return nil, err
 	}
 
 	// map each relevant field in inspectResponse to the mapped field from the config
 	var inspectResponse InspectResponse
 	inspectResponse.UserID, _ = genericInterface[c.MapUserID].(string)
+	if inspectResponse.UserID == "" {
+		log.Error("[CONFIGURATION ERROR] Generic OAuth provider returned empty UserID value (`%s`).\n  Do you need to configure a different `map_user_id` value for this provider?", c.MapUserID)
+		return nil, fmt.Errorf("no UserID (`%s`) value returned", c.MapUserID)
+	}
 	inspectResponse.Username, _ = genericInterface[c.MapUsername].(string)
 	inspectResponse.DisplayName, _ = genericInterface[c.MapDisplayName].(string)
 	inspectResponse.Email, _ = genericInterface[c.MapEmail].(string)
 
 	return &inspectResponse, nil
 }