Python脚本调用Gmail API报错：web类型客户端缺失redirect_uris

Hey there, let's unpack what's happening with your Gmail script and that pesky error.

First, let's get to the root of the issue: Google's OAuth2 framework requires the redirect_uris field for "Web application" type client IDs. This isn't a random quirk of the oauth2client library—it's part of the official OAuth2 spec for web apps, which rely on redirects to complete the authorization flow.

Why your script worked before #

Chances are, your original client_secret.json was tied to a Desktop app type client ID (not a Web application). Desktop/script-based apps have different OAuth2 rules—they don't need a custom redirect URI (Google uses a default value like urn:ietf:wg:oauth:2.0:oob for terminal-based auth) and the oauth2client library doesn't enforce the redirect_uris field for this type.

Possible reasons it broke now:

• You might have recreated your client ID in Google Cloud Console and accidentally selected "Web application" instead of "Desktop app".
• You updated the oauth2client library to a newer version that enforces stricter validation of client secret fields for Web app types.

How to fix this #

You have two solid options:

Option 1: Switch to a Desktop app client ID (recommended for local scripts)

This is the cleanest fix since you don't need redirects for a local script:

1. Go to your Google Cloud Console Credentials page
2. Either delete your existing "Web application" client ID or create a new one
3. Create a new OAuth client ID, select Desktop app as the application type
4. Download the new client_secret.json and replace your current file
5. Your script should work as it did before—no need to add redirect_uris at all

Option 2: Keep using Web app type (if you have to)

If you must stick with a Web app client ID, you need to keep the redirect_uris field in your client_secret.json—even if you don't actively use the redirect. You can use a placeholder valid for local testing:

{
  "web": {
    "client_id": "your-client-id",
    "client_secret": "your-client-secret",
    "redirect_uris": ["http://localhost:8000"],
    "auth_uri": "https://accounts.google.com/o/oauth2/auth",
    "token_uri": "https://oauth2.googleapis.com/token"
  }
}

The library just needs this field to exist and have a valid URI format—you don't need to run a server at that localhost address for a simple send-only script.

Quick code check #

Make sure your flow initialization aligns with the client type. For Desktop apps, the standard setup looks like this:

from oauth2client import client, tools
from oauth2client.file import Storage

CLIENT_SECRET_FILE = 'client_secret.json'
SCOPES = ['https://www.googleapis.com/auth/gmail.send']

def get_credentials():
    storage = Storage('gmail-token.json')
    credentials = storage.get()
    if not credentials or credentials.invalid:
        flow = client.flow_from_clientsecrets(CLIENT_SECRET_FILE, SCOPES)
        credentials = tools.run_flow(flow, storage)
    return credentials

This will handle the authorization flow in your terminal (or pop up a browser window) without needing a redirect server.

内容的提问来源于stack exchange，提问作者codyc4321