📝 Add tutorial for complete OAuth2 password flow

docs/src/security/tutorial003.py

@@ -1,5 +1,3 @@
-from typing import Optional
-
 from fastapi import Depends, FastAPI, Security
 from fastapi.security import OAuth2PasswordBearer, OAuth2PasswordRequestForm
 from pydantic import BaseModel
@@ -10,7 +8,8 @@ fake_users_db = {
         "username": "johndoe",
         "full_name": "John Doe",
         "email": "[email protected]",
-        "password_hash": "fakehashedsecret",
+        "hashed_password": "fakehashedsecret",
+        "disabled": False,
     }
 }
 
@@ -26,9 +25,9 @@ oauth2_scheme = OAuth2PasswordBearer(tokenUrl="/token")
 
 class User(BaseModel):
     username: str
-    email: Optional[str] = None
-    full_name: Optional[str] = None
-    disabled: Optional[bool] = None
+    email: str = None
+    full_name: str = None
+    disabled: bool = None
 
 
 class UserInDB(User):
@@ -51,26 +50,28 @@ def fake_decode_token(token):
 async def get_current_user(token: str = Security(oauth2_scheme)):
     user = fake_decode_token(token)
     if not user:
-        raise HTTPException(status_code=400, detail="Inactive user")
+        raise HTTPException(
+            status_code=400, detail="Invalid authentication credentials"
+        )
     return user
 
 
 async def get_current_active_user(current_user: User = Depends(get_current_user)):
-    if not current_user.disabled:
+    if current_user.disabled:
         raise HTTPException(status_code=400, detail="Inactive user")
     return current_user
 
 
 @app.post("/token")
-async def login(form_data: OAuth2PasswordRequestForm):
+async def login(form_data: OAuth2PasswordRequestForm = Depends()):
     data = form_data.parse()
-    user_dict = fake_users_db[data.username]
+    user_dict = fake_users_db.get(data.username)
+    if not user_dict:
+        raise HTTPException(status_code=400, detail="Incorrect username or password")
     user = UserInDB(**user_dict)
-    if not user:
-        raise HTTPException(status_code=400, detail="Incorrect email or password")
     hashed_password = fake_hash_password(data.password)
     if not hashed_password == user.hashed_password:
-        raise HTTPException(status_code=400, detail="Incorrect email or password")
+        raise HTTPException(status_code=400, detail="Incorrect username or password")
 
     return {"access_token": user.username, "token_type": "bearer"}
 

docs/tutorial/security/simple-oauth2.md

@@ -1,5 +1,211 @@
-Coming soon...
+Now let's build from the previous chapter and add the missing parts to have a complete security flow.
+
+## Get the `username` and `password`
+
+We are going to use **FastAPI** security utilities to get the `username` and `password`.
+
+OAuth2 specifies that when using the "password flow" (that we are using) the client / user must send a `username` and `password` fields as form data.
+
+And the spec says that the fields have to be named like that. So `user-name` or `email` wouldn't work.
+
+But don't worry, you can show it as you wish to your final users in the frontend.
+
+And your database models can use any other names you want.
+
+But for the login path operation, we need to use these names to be compatible with the spec (and be able to, for example, use the integrated API documentation system).
+
+The spec also states that the `username` and `password` must be sent as form data (so, no JSON here).
+
+### `scopes`
+
+The spec also says that the client can send another field of "`scopes`".
+
+As a long string with all these "scopes" separated by spaces.
+
+Each "scope" is just a string.
+
+They are normally used to declare specific security permissions, for exampe:
+
+* `"users:read"` or `"users:write"` are common examples.
+* `instagram_basic` is used by Facebook / Instagram.
+* `https://www.googleapis.com/auth/drive` is used by Google.
+
+!!! info
+    In OAuth2 a "scope" is just a string that declares a specific permision required.
+
+    It doesn't matter if it has other characters like `:`, or if it is a URL.
+    
+    Those details are implementation specific.
+
+    For OAuth2 they are just strings.
+
+    And when using `scopes` it normally referes to a long string of "scopes" separated by spaces.
+
+
+## Code to get the `username` and `password`
+
+Now let's use the utilities provided by **FastAPI** to handle this.
+
+### `OAuth2PasswordRequestForm`
+
+First, import `OAuth2PasswordRequestForm`, and use it as the body declaration of the path `/token`:
+
+```Python hl_lines="2 63"
+{!./src/security/tutorial003.py!}
+```
+
+`OAuth2PasswordRequestForm` declares a form body with:
+
+* The `username`.
+* The `password`.
+* An optional `scopes` field as a big string, composed of strings separated by spaces.
+* An optional `grant_type`.
+
+!!! tip
+    The OAuth2 spec actually *requires* a field `grant_type` with a fixed value of `password`, but `OAuth2PasswordRequestForm` doesn't enforce it.
+
+    If you need to enforce it, use `OAuth2PasswordRequestFormStrict` instead of `OAuth2PasswordRequestForm`.
+
+* An optional `client_id` (we don't need it for our example).
+* An optional `client_secret` (we don't need it for our example).
+
+### Parse and use the form data
+
+`OAuth2PasswordRequestForm` provides a `.parse()` method that converts the `scopes` string into an actual list of strings.
+
+We are not using `scopes` in this example, but the functionality is there if you need it.
+
+!!! tip
+    The `.parse()` method returns a Pydantic model `OAuth2PasswordRequestData`.
+
+    But you don't need to import it, your editor will know its type and provide you with completion and type checks automatically.
+
+Now, get the user data from the (fake) database, using this `username`.
+
+If there is no such user, we return an error saying "incorrect username or password".
+
+For the error, we use the exception `HTTPException` provided by Starlette directly:
+
+```Python hl_lines="4 64 65 66 67"
+{!./src/security/tutorial003.py!}
+```
+
+### Check the password
+
+At this point we have a the user data from our database, but we haven't checked the password.
+
+Let's put that data in the Pydantic `UserInDB` model first.
+
+You should never save plaintext passwords, so, we'll use the (fake) password hashing system.
+
+If the password doesn't match, we return the same error.
+
+```Python hl_lines="68 69 70 71"
+{!./src/security/tutorial003.py!}
+```
+
+#### About `**user_dict`
+
+`UserInDB(**user_dict)` means:
+    
+Pass the keys and values of the `user_dict` directly as key-value arguments, equivalent to:
 
 ```Python
+UserInDB(
+    username=user_dict["username"],
+    email=user_dict["email"],
+    full_name=user_dict["full_name"],
+    disabled=user_dict["disabled"],
+    hashed_password=user_dict["hashed_password"],
+)
+```
+
+## Return the token
+
+The response of the `token` endpoint must be a JSON object.
+
+It should have a `token_type`. In our case, as we are using "Bearer" tokens, the token type should be `bearer`.
+
+And it should have an `access_token`, with a string containing our access token.
+
+For this simple example, we are going to just be completely insecure and return the same `username` as the token.
+
+!!! tip
+    In the next chapter, you will see a real secure implementation, with password hasing and JWT tokens.
+
+    But for now, let's focus on the specific details we need.
+
+```Python hl_lines="73"
+{!./src/security/tutorial003.py!}
+```
+
+## Update the dependencies
+
+Now we are going to update our dependencies.
+
+We want to get the `current_user` *only* if this user is active.
+
+So, we create an additional dependency `get_current_active_user` that in turn uses `get_current_user` as a dependency.
+
+Both of these dependencies will just return an HTTP error if the user doesn't exists, or if is inactive.
+
+So, in our endpoint, we will only get a user if the user exists, was correctly authenticated, and is active:
+
+```Python hl_lines="49 50 51 52 53 56 57 58 59 77"
 {!./src/security/tutorial003.py!}
 ```
+
+## See it in action
+
+Open the interactive docs: <a href="http://127.0.0.1:8000/docs" target="_blank">http://127.0.0.1:8000/docs</a>.
+
+### Authenticate
+
+Click the "Authorize" button.
+
+Use the credentials:
+
+User: `johndoe`
+Password: `secret`
+
+<img src="/img/tutorial/security/image04.png">
+
+After authenticating in the system, you will see it like:
+
+<img src="/img/tutorial/security/image05.png">
+
+### Get your own user data
+
+Now use the operation `GET` with the path `/users/me`.
+
+You will get your user's data, like:
+
+```JSON
+{
+  "username": "johndoe",
+  "email": "[email protected]",
+  "full_name": "John Doe",
+  "disabled": false,
+  "hashed_password": "fakehashedsecret"
+}
+```
+
+<img src="/img/tutorial/security/image06.png">
+
+If you click the lock icon and logout, and then try the same operation again, you will get an HTTP 403 error of:
+
+```JSON
+{
+  "detail": "Not authenticated"
+}
+```
+
+## Recap
+
+You now have the tools to implement a complete security system based on `username` and `password` for your API.
+
+Using these tools, you can make the security system compatible with any database and with any user or data model.
+
+The only detail missing is that it is not actually "secure" yet.
+
+In the next chapter you'll see how to use a secure password hashing library and JWT tokens.