您需要了解Web应用程序和已安装的应用程序之间存在差异。已安装的应用程序将在用户使用它的计算机上运行。同意屏幕在该机器上打开。Web应用程序需要在用户浏览器而不是Web服务器上打开同意屏幕。这些类型的客户端是不同的安装应用程序不需要有一个重定向URI它总是127.0.0.1，一个Web应用程序需要允许您包括重定向URI到您的网站。因此，这两种类型的客户端的代码是不同的。您正在跟踪的示例是针对已安装的应用程序的，它不会在托管中工作。
下面是我使用flask进行web auth的基本示例。

# https://github.com/googleads/googleads-python-lib/wiki/API-access-on-behalf-of-your-clients-%28web-flow%29
import os

import flask
from flask import Flask,redirect,render_template,url_for, request
app = Flask(__name__, template_folder='templates')
import google.auth.exceptions
import google_auth_oauthlib.flow
import ssl
context = ssl.SSLContext()
context.load_cert_chain('C:\Development\FreeLance\GoogleSamples\Python\cert.pem', 'C:\Development\FreeLance\GoogleSamples\Python\key.pem')
from google.oauth2.credentials import Credentials
from google.auth.transport.requests import Request
from googleapiclient.errors import HttpError
from googleapiclient.discovery import build
import google_auth_oauthlib.flow

SCOPES = ['https://mail.google.com/']

REDIRECT_URI = 'https://127.0.0.1:5000/oauth2callback'

CREDENTIALS = 'C:\Development\FreeLance\GoogleSamples\Credentials\CredWebEverything.json'

def get_flow():

    # Initialize the flow using the client ID and secret downloaded earlier.
    flow = google_auth_oauthlib.flow.Flow.from_client_secrets_file(
        CREDENTIALS,
        scopes= SCOPES,
    )
    # Indicate where the API server will redirect the user after the user completes
    # the authorization flow. The redirect URI is required.
    flow.redirect_uri = REDIRECT_URI

    return flow

def redirect_user():

    flow = get_flow()
    # Generate URL for request to Google's OAuth 2.0 server.
    # Use kwargs to set optional request parameters.
    authorization_url, state = flow.authorization_url(
        # Enable offline access so that you can refresh an access token without
        # re-prompting the user for permission. Recommended for web server apps.
        access_type='offline',
        # Enable incremental authorization. Recommended as a best practice.
        include_granted_scopes='false',
        # Forces a new refresh token when we authorize the application a second time.
        #prompt= "consent"
        )

    return authorization_url, state

@app.route('/login')
def login():
    authorization_url, state = redirect_user()
    return flask.redirect(authorization_url)

@app.route('/listmessages')
def gmail_list_messages():
    creds = None
    # The file token.json stores the user's access and refresh tokens, and is
    # created automatically when the authorization flow completes for the first
    # time.
    if os.path.exists('token.json'):
        try:
            creds = Credentials.from_authorized_user_file('token.json', SCOPES)
            print(f'Credentials exist refreshing.')
            creds.refresh(Request())
        except google.auth.exceptions.RefreshError as error:
            # if refresh token fails, reset creds to none.
            creds = None
            print(f'An error occurred: {error}')
    # If there are no (valid) credentials available, let the user log in.
    if not creds or not creds.valid:
        if creds and creds.expired and creds.refresh_token:
            creds.refresh(Request())
        else:
            # If it's not logged in then it's going to force it to.
            authorization_url, state = redirect_user()
            print(f'Credentials do not exist requesting authorization.')
            return flask.redirect(authorization_url)
    try:
        service = build('gmail', 'v1', credentials=creds)

        # Call the Gmail v1 API
        results = service.users().messages().list(
            userId='me').execute()
        messages = results.get('messages', [])
    except HttpError as error:
        # TODO(developer) - Handle errors from gmail API.
        print(f'An error occurred: {error}')

    return render_template("mail.html", data=messages)


@app.route('/')
def index():
    return render_template('index.html', title="Home Page")

@app.route('/oauth2callback')
def oauth2callback():
    flow = get_flow()

    auth_code = request.args['code']
    flow.fetch_token(code=auth_code)
    credentials = flow.credentials

    # saving the credentials for later. Note: A refresh does not return a new refresh token.
    if not os.path.exists('token.json') or credentials.refresh_token:
        print(f'Storing credentials: {credentials.to_json()}')
        with open('token.json', 'w') as token:
            token.write(credentials.to_json())

    return redirect("/listmessages")

if __name__ == '__main__':
    # Bind to PORT if defined, otherwise default to 5000.
    port = int(os.environ.get('PORT', 5000))
    app.run(host='0.0.0.0', port=port, ssl_context=context)