You could also use `from starlette.middleware.cors import CORSMiddleware`.

**FastAPI** provides several middlewares in `fastapi.middleware` just as a convenience for you, the developer. But most of the available middlewares come directly from Starlette.

Let's use the tools provided by **FastAPI** to handle security.

## How it looks { #how-it-looks }

Let's first just use the code and see how it works, and then we'll come back to understand what's happening.

## Create `main.py` { #create-main-py }

Copy the example in a file `main.py`:

{* ../../docs_src/security/tutorial001_an_py39.py *}

## Run it { #run-it }

/// info

    checkNotNull(keyFunction);
    checkNotNull(valueFunction);
    /*
     * We will always fail if there are duplicate keys, and the keys are always sorted by
     * the Comparator, so the entries can come in an arbitrary order -- so we report UNORDERED.
     */
    return Collector.of(
        () -> new ImmutableSortedMap.Builder<K, V>(comparator),

    checkNotNull(keyFunction);
    checkNotNull(valueFunction);
    /*
     * We will always fail if there are duplicate keys, and the keys are always sorted by
     * the Comparator, so the entries can come in an arbitrary order -- so we report UNORDERED.
     */
    return Collector.of(
        () -> new ImmutableSortedMap.Builder<K, V>(comparator),

        assertTrue(pattern.contains("token"));
        assertTrue(pattern.contains("secret"));
    }

    // Test array field parsing
    public void test_arrayFieldParsing() {
        // Test parsing of comma-separated values
        String[] arrayFields = fessConfig.getIndexAdminArrayFields().split(",");
        assertNotNull(arrayFields);
        assertEquals(2, arrayFields.length);

 * degrades more gracefully for worst-case input.
 *
 * <p>The implementation does not necessarily use a <i>stable</i> sorting algorithm; when multiple
 * equivalent elements are added to it, it is undefined which will come first in the output.
 *
 * @author Louis Wasserman
 */
@GwtCompatible
final class TopKSelector<
    T extends @Nullable Object> {

  /**

    String ID_COMBINATION_MODE_ATTRIBUTE = XmlService.ID_COMBINATION_MODE_ATTRIBUTE;

    /**
     * In case of complex XML structures, combining can be done based on keys.
     * This is a comma separated list of attribute names.
     */
    @Deprecated(since = "4.0.0", forRemoval = true)
    String KEYS_COMBINATION_MODE_ATTRIBUTE = XmlService.KEYS_COMBINATION_MODE_ATTRIBUTE;

    /**

The whole **FastAPI** framework is based to satisfy that. Autocompletion works everywhere.

You will rarely need to come back to the docs.

Here's how your editor might help you:

* in <a href="https://code.visualstudio.com/" class="external-link" target="_blank">Visual Studio Code</a>:

1F101         ; disallowed_STD3_mapped ; 0030 002C     # 5.2  DIGIT ZERO COMMA
1F102         ; disallowed_STD3_mapped ; 0031 002C     # 5.2  DIGIT ONE COMMA
1F103         ; disallowed_STD3_mapped ; 0032 002C     # 5.2  DIGIT TWO COMMA
1F104         ; disallowed_STD3_mapped ; 0033 002C     # 5.2  DIGIT THREE COMMA
1F105         ; disallowed_STD3_mapped ; 0034 002C     # 5.2  DIGIT FOUR COMMA

				<-keepAliveTicker.C
			}
		}
	}

	// On Kubernetes/Docker setups DNS resolves inappropriately sometimes
	// where there are situations same endpoints with multiple disks
	// come online indicating either one of them is local and some
	// of them are not local. This situation can never happen and
	// its only a possibility in orchestrated deployments with dynamic