Header photo by fabio on Unsplash
In the last post we looked at how to enable two-factor authentication with FastAPI using pyotp. We looked at some areas we might explore how to improve on the v1 implementation. In this post we will be updating the implementation to include:
- A backend user database (in this case SQLite).
- Functionality to add a new user.
- Functionality for the user to update their data.
This is based on the FastAPI docs for SQL (Relational) Databases.
As part of this application, we will be using the SQLAlchemy ORM (Object Relational Mapping) toolkit to interact with a backend SQL database. SQLAlchemy helps to achieve a consistent relationship between the object representation in Python and data storage in SQL. Using SQLAlchemy, we can manipulate the objects directly in Python which are then reflected in the SQL database. To install SQLAlchemy you can run pip install SQLAlchemy from the command line.
Clone the Repo
The code for this tutorial can all be found in the v2 directory in the github repo. You will see some other .py files have been added:
database.pymodels.pyschemas.pycrud.pysecurity.py
The database.py is taken from the tutorial example in the FastAPI docs and I have kept it almost exactly the same aside from changing the SQLALCHEMY_DATABASE_URL.
The models.py file describes the database structure, the tables and (if any) the relationships between the tables. In here we will declare the table name and columns that are in the user table along with their type and any default values.
Next, the schemas that were originally in main.py has now been moved into it’s own schemas.py file. The User schemas have been separated by read, write, read/write and update. There are currently two role types that can be used; admin and user. You can add others if you wish, for example “moderator”.
The crud.py file contains the helper functions used to query the database. CRUD stands for Create, Read, Update, Delete. Keeping these functions together in a separate file prevents code duplication and simplifies maintenance. For this example, there is create, read and update but, at this point, no delete. In main.py we have the functions that determine the endpoints of the API, which can utilise the functions defined in crud.py.
To run the code, type uvicorn main:app --reload and open the docs page.
Connect to the SQLite database
When you run the code, you should see a .db file is created, in this case it is called twofactor_app.db. This is the file that contains the data in the SQLite database. To interact with and view this data you can install the SQLite browser, which is freely available here.
Once installed, you can click on Open Database and then select the .db file from the directory. Initially, you will see a database with no records.
Creating new users
In the last tutorial, there was no way to create new users, aside from hardcoding them into the main.py script. The code has now been extended to enable new users to be added by posting to the /users endpoint.
In the crud.py file you will see a new function, which enables the details for a new user to be added. The password entered will be hashed and a random otp_secret (which we used to generate the QR code in the previous post) is generated as part of the code. Once a change has been implemented, we also need to commit changes using the db.commit() function.
#crud.py
def create_user(db: Session, user: schemas.UserCreate):
hashed_password = pwd_context.hash(user.password)
db_user = models.User(
email=user.email,
username=user.username,
full_name=user.full_name,
hashed_password=hashed_password,
otp_secret=pyotp.random_base32(),
role=user.role
)
db.add(db_user)
db.commit()
db.refresh(db_user)
return db_user
It has been set up so that only an admin can create a new user. As there are no current users, we will need to manually add an initial user, which I will explain how to do.
In the main.py code, you will see that there is a new function def get_current_active_admin_user in which, if the user logged in is not admin it will return a permissions error. This dependency is shown highlighted in the code for creating a new user in main.py
@app.post("/users/", response_model=schemas.User)
def create_new_user(
user: schemas.UserCreate,
db: Session = Depends(get_db),
current_user: schemas.User = Depends(get_current_active_admin_user)):
db_user = crud.create_user(db, user)
return db_user
To add an initial user to the database, use the SQLite browser tool. To add a new record, click on the add a new record symbol in the menu as shown in the following screenshot:
Input the following values into the columns:
{
"username": "johndoe",
"email": "johndoe@example.com",
"full_name": "John Doe",
"hashed_password": "$2b$12$rMFOsKHq6qaX6bbPB0pb6.ymbwF63soIe19af9qd.1Q8PhbCVfXSO", //this password has already been hashed
"otp_secret": "LGLEREYEPVVWTLYO",
"disabled": 0,
"role": "admin"
}
Click on “Write Changes” to commit the changes.
Click on the refresh symbol and you will see the new user has been added.
You will now be able to log in in the same way as shown in the previous post using two-factor authentication. Once logged in with an admin user you will be able to create new users using a POST request to the /user endpoint.
To try out creating a new user, click on the POST /users create new user endpoint on the FastAPI application docs page. Click on “Try it out” and then input the following example request body. Click on the “Execute” button.
{
"username": "alicewonderland",
"email": "alicewonderland@example.com",
"full_name": "Alice Wonderland",
"password": "whiterabbit"
}
User Operations
The v2 directory code now includes the ability for a user to:
- read their own data information or that of another user (if admin).
- update their own data
The following endpoints (other than create new user, which was mentioned in the previous section) are now available to use:
GET /users/me – dependent on a user being logged in. If this dependency is fulfilled, this request will return the user details in the response body.
PUT /users/me – dependent on a user being logged in. If this dependency is fulfilled, user can update their own user data and these changes will be updated in the SQLite user database.
GET /users/{user_id} – dependent on a user being logged in and admin. If this dependency is fulfilled, admin users can get the user data for a user based on their user_id.
In the next installment, I will cover how we can make some more improvements so stay tuned! If there is something you are specifically interested in learning about FastAPI, feel free to leave it in the comments.
I had a few issues along the way (many due to my own errors :p). One thing I noticed is that my microbit was a bit sensitive and kept disconnecting from the power source every few minutes, I tried with another which seemed much more stable. 
Developing For Data 