# Security - First Steps { #security-first-steps }

Let's imagine that you have your **backend** API in some domain.

And you have a **frontend** in another domain or in a different path of the same domain (or in a mobile application).

And you want to have a way for the frontend to authenticate with the backend, using a **username** and **password**.

We can use **OAuth2** to build that with **FastAPI**.

        assertNotNull(result, "Unwrapped tree should not be null");
        assertSame(customTree, result, "Should return the same custom tree instance");
        verify(smbTree).unwrap(CustomSmbTree.class);
    }

    /**
     * Test for unwrap() method with the same type.
     * Verifies that unwrap can return itself when the type matches.
     */
    @Test
    void testUnwrap_withSameType() {

   * exactly one entry for each distinct element in the multiset (thus it always has the same size
   * as the {@link #elementSet}). The order of the elements in the element set is unspecified.
   *
   * <p>The entry set is backed by the same data as the multiset, so any change to either is
   * immediately reflected in the other. However, multiset changes may or may not be reflected in

## Read the Tutorial first { #read-the-tutorial-first }

The next sections assume you already read the main [Tutorial - User Guide: Security](../../tutorial/security/index.md){.internal-link target=_blank}.

   */
  public final FluentIterable<E> skip(int numberToSkip) {
    return from(Iterables.skip(getDelegate(), numberToSkip));
  }

  /**
   * Creates a fluent iterable with the first {@code size} elements of this fluent iterable. If this
   * fluent iterable does not contain that many elements, the returned fluent iterable will have the

You can re-raise the same exception using `raise`:

{* ../../docs_src/dependencies/tutorial008d_an_py39.py hl[17] *}

Now the client will get the same *HTTP 500 Internal Server Error* response, but the server will have our custom `InternalError` in the logs. 😎

	STREX	R1, (R0), R1       // ERROR "cannot use same register as both source and destination"
	STREX	R1, (R0), R0       // ERROR "cannot use same register as both source and destination"
	STREXD	R0, (R2), R0       // ERROR "cannot use same register as both source and destination"
	STREXD	R0, (R2), R1       // ERROR "cannot use same register as both source and destination"
	STREXD	R0, (R2), R2       // ERROR "cannot use same register as both source and destination"

    }

    @Test
    @DisplayName("getSmbTree returns same instance for same share/service")
    void testGetSmbTreeReuses() {
        SmbSessionImpl session = newSession();
        SmbTreeImpl t1 = session.getSmbTree("IPC$", null);
        SmbTreeImpl t2 = session.getSmbTree("ipc$", null); // case-insensitive match
        assertSame(t1, t2, "Expected same tree instance to be reused");
    }

    @ParameterizedTest

The same as when using a custom CDN, the first step is to disable the automatic docs, as those use the CDN by default.

To disable them, set their URLs to `None` when creating your `FastAPI` app:

{* ../../docs_src/custom_docs_ui/tutorial002_py39.py hl[9] *}

### Include the custom docs for static files { #include-the-custom-docs-for-static-files }

                should have all the fields, including the ones that have the same value
                as the default. This is different from `response_model_exclude_unset`
                in that if the fields are set but contain the same default values,
                they will be excluded from the response.