again:--

  `I didn't know that Cheshire cats always grinned; in fact, I
didn't know that cats COULD grin.'

  `They all can,' said the Duchess; `and most of 'em do.'

  `I don't know of any that do,' Alice said very politely,
feeling quite pleased to have got into a conversation.

  `You don't know much,' said the Duchess; `and that's a fact.'

Now you know that whenever you need them you can use them in **FastAPI**.

### Pydantic v1 `regex` instead of `pattern` { #pydantic-v1-regex-instead-of-pattern }

Before Pydantic version 2 and before FastAPI 0.100.0, the parameter was called `regex` instead of `pattern`, but it's now deprecated.

You could still see some code using it:

//// tab | Pydantic v1

But then we get a `dict` in the parameter `commons` of the *path operation function*.

And we know that editors can't provide a lot of support (like completion) for `dict`s, because they can't know their keys and value types.

We can do better...

## What makes a dependency { #what-makes-a-dependency }

Up to now you have seen dependencies declared as functions.

These examples are intentionally simple, but show how it all works.

In the chapters about security, there are utility functions that are implemented in this same way.

If you understood all this, you already know how those utility tools for security work underneath.

FB13          ; mapped                 ; 0574 0576     # 1.1  ARMENIAN SMALL LIGATURE MEN NOW
FB14          ; mapped                 ; 0574 0565     # 1.1  ARMENIAN SMALL LIGATURE MEN ECH
FB15          ; mapped                 ; 0574 056B     # 1.1  ARMENIAN SMALL LIGATURE MEN INI
FB16          ; mapped                 ; 057E 0576     # 1.1  ARMENIAN SMALL LIGATURE VEW NOW

* The encryption of the connection happens at the **TCP level**.
    * That's one layer **below HTTP**.
    * So, the **certificate and encryption** handling is done **before HTTP**.
* **TCP doesn't know about "domains"**. Only about IP addresses.
    * The information about the **specific domain** requested goes in the **HTTP data**.

The **server** program (for example **Uvicorn** via **FastAPI CLI**) is capable of interpreting these headers, and then passing that information to your application.

{* ../../docs_src/security/tutorial005_an_py310.py hl[5,9,13,47,65,106,108:116,122:126,130:136,141,157] *}

Now let's review those changes step by step.

## OAuth2 Security scheme { #oauth2-security-scheme }

The first change is that now we are declaring the OAuth2 security scheme with two available scopes, `me` and `items`.

**FastAPI** will know that it can use the class `OAuth2PasswordBearer` (declared in a dependency) to define the security scheme in OpenAPI because it inherits from `fastapi.security.oauth2.OAuth2`, which in turn inherits from `fastapi.security.base.SecurityBase`.

All the security utilities that integrate with OpenAPI (and the automatic API docs) inherit from `SecurityBase`, that's how **FastAPI** can know how to integrate them in OpenAPI.

    By having the type as `int | None`, SQLModel will know that this column should be an `INTEGER` in the SQL database and that it should be `NULLABLE`.

* `Field(index=True)` tells SQLModel that it should create a **SQL index** for this column, that would allow faster lookups in the database when reading data filtered by this column.