Authentication and Client Creation

By now, you should have followed the instructions in Getting Started and are ready to start making API calls. Read this page to learn how to get over the last remaining hurdle: OAuth authentication.

Before we begin, however, note that this guide is meant to users who want to run applications on their own machines, without distributing them to others. If you plan on distributing your app, or if you plan on running it on a server and allowing access to other users, this login flow is not for you.

OAuth Refresher

This section is purely for the curious. If you already understand OAuth (wow, congrats) or if you don’t care and just want to use this package as fast as possible, feel free to skip this section. If you encounter any weird behavior, this section may help you understand what’s going on.

Webapp authentication is a complex beast. The OAuth protocol was created to allow applications to access one anothers’ APIs securely and with the minimum level of trust possible. A full treatise on this topic is well beyond the scope of this guide, but in order to alleviate some of the complexity that seems to surround this part of the API, let’s give a quick explanation of how OAuth works in the context of Schwab’s API.

The first thing to understand is that the OAuth webapp flow was created to allow client-side applications consisting of a webapp frontend and a remotely hosted backend to interact with a third party API. Unlike the backend application flow, in which the remotely hosted backend has a secret which allows it to access the API on its own behalf, the webapp flow allows either the webapp frontend or the remotely host backend to access the API on behalf of its users.

If you’ve ever installed a GitHub, Facebook, Twitter, GMail, etc. app, you’ve seen this flow. You click on the “install” link, a login window pops up, you enter your password, and you’re presented with a page that asks whether you want to grant the app access to your account.

Here’s what’s happening under the hood. The window that pops up is the authentication URL, which opens a login page for the target API. The aim is to allow the user to input their username and password without the webapp frontend or the remotely hosted backend seeing it. On web browsers, this is accomplished using the browser’s refusal to send credentials from one domain to another.

Once login here is successful, the API replies with a redirect to a URL that the remotely hosted backend controls. This is the callback URL. This redirect will contain a code which securely identifies the user to the API, embedded in the query of the request.

You might think that code is enough to access the API, and it would be if the API author were willing to sacrifice long-term security. The exact reasons why it doesn’t work involve some deep security topics like robustness against replay attacks and session duration limitation, but we’ll skip them here.

This code is useful only for fetching a token from the authentication endpoint. This token is what we want: a secure secret which the client can use to access API endpoints, and can be refreshed over time.

If you’ve gotten this far and your head isn’t spinning, you haven’t been paying attention. Security-sensitive protocols can be very complicated, and you should never build your own implementation. Fortunately there exist very robust implementations of this flow, and schwab-py’s authentication module makes using them easy.

Fetching a Token and Creating a Client

Once you have a token written on disk, you can reuse it without going through the login flow again.

schwab.auth.client_from_token_file(token_path, api_key, app_secret, asyncio=False, enforce_enums=True)

Returns a session from an existing token file. The session will perform an auth refresh as needed. It will also update the token on disk whenever appropriate.

Parameters:

token_path – Path to an existing token. Updated tokens will be written to this path. If you do not yet have a token, use client_from_login_flow() or easy_client() to create one.
api_key – Your Schwab application’s app key.
app_secret – Application secret. Provided upon app approval.
asyncio – If set to True, this will enable async support allowing the client to be used in an async environment. Defaults to False
enforce_enums – Set it to False to disable the enum checks on ALL the client methods. Only do it if you know you really need it. For most users, it is advised to use enums to avoid errors.

If you don’t want to create a client and just want to fetch a token, you can use the schwab-generate-token.py script that’s installed with the library. This method is particularly useful if you want to create your token on one machine and use it on another.

# Notice we don't prefix this with "python" because this is a script that was
# installed by pip when you installed schwab-py
> schwab-generate-token.py --help
usage: schwab-generate-token.py [-h] --token_file TOKEN_FILE --api_key API_KEY
--redirect_uri REDIRECT_URI

Fetch a new token and write it to a file

optional arguments:
  -h, --help            show this help message and exit

required arguments:
  --token_file TOKEN_FILE
                      Path to token file. Any existing file will be overwritten
  --api_key API_KEY
  --redirect_uri REDIRECT_URI

This script is installed by pip, and will only be accessible if you’ve added pip’s executable locations to your $PATH. If you’re having a hard time, feel free to ask for help on our Discord server.

Advanced Functionality

The default token fetcher functions are designed for ease of use. They make some common assumptions, most notably a writable filesystem, which are valid for 99% of users. However, some very specialized users, for instance those hoping to deploy schwab-py in serverless settings, require some more advanced functionality. This method provides the most flexible facility for fetching tokens possible.

Important: This is an extremely advanced method. If you read the documentation and think anything other than “oh wow, this is exactly what I’ve been looking for,” you don’t need this function. Please use the other helpers instead.

schwab.auth.client_from_access_functions(api_key, app_secret, token_read_func, token_write_func, asyncio=False, enforce_enums=True)

Returns a session from an existing token file, using the accessor methods to read and write the token. This is an advanced method for users who do not have access to a standard writable filesystem, such as users of AWS Lambda and other serverless products who must persist token updates on non-filesystem places, such as S3. 99.9% of users should not use this function.

Users are free to customize how they represent the token file. In theory, since they have direct access to the token, they can get creative about how they store it and fetch it. In practice, it is highly recommended to simply accept the token object and use json to serialize and deserialize it, without inspecting it in any way.

Note the read and write methods must take particular arguments. Please see this example for details.

Parameters:

api_key – Your Schwab application’s app key.
app_secret – Application secret. Provided upon app approval.
token_read_func – Function that takes no arguments and returns a token object.
token_write_func – Function that writes the token on update. Will be called whenever the token is updated, such as when it is refreshed. See the above-mentioned example for what parameters this method takes.
asyncio – If set to True, this will enable async support allowing the client to be used in an async environment. Defaults to False
enforce_enums – Set it to False to disable the enum checks on ALL the client methods. Only do it if you know you really need it. For most users, it is advised to use enums to avoid errors.

Troubleshooting

As simple as it seems, this process is complex and mistakes are easy to make. This section outlines some of the more common issues you might encounter. If you find yourself dealing with something that isn’t listed here, or if you try the suggested remedies and are still seeing issues, see the Getting Help page. You can also join our Discord server to ask questions.

Token Parsing Failures

schwab-py handles creating and refreshing tokens. Simply put, the user should never create or modify the token file. If you are experiencing parse errors when accessing the token file or getting exceptions when accessing it, it’s probably because you created it yourself or modified it. If you’re experiencing token parsing issues, remember that:

You should never create the token file yourself. If you don’t already have a token, you should pass a nonexistent file path to client_from_login_flow() or easy_client(). If the file already exists, these methods assume it’s a valid token file. If the file does not exist, they will go through the login flow to create one.
You should never modify the token file. The token file is automatically managed by schwab-py, and modifying it will almost certainly break it.
You should never share the token file. If the token file is shared between applications, one of them will beat the other to refreshing, locking the slower one out of using schwab-py.

If you didn’t do any of this and are still seeing issues using a token file that you’re confident is valid, please file a ticket. Just remember, never share your token file, not even with schwab-py developers. Sharing the token file is as dangerous as sharing your Schwab username and password.