Just functions that look the same as the *path operation functions*.

But still, it is very powerful, and allows you to declare arbitrarily deeply nested dependency "graphs" (trees).

/// tip

All this might not seem as useful with these simple examples.

But you will see how useful it is in the chapters about **security**.

And you will also see the amounts of code it will save you.

For example, Google login uses OpenID Connect (which underneath uses OAuth2).

But Facebook login doesn't support OpenID Connect. It has its own flavor of OAuth2.

### OpenID (not "OpenID Connect") { #openid-not-openid-connect }

There was also an "OpenID" specification. That tried to solve the same thing as **OpenID Connect**, but was not based on OAuth2.

So, it was a complete additional system.

// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//

    /**
     * Gets the decrypted proxies.
     *
     * @return The decrypted proxy, can be empty but never {@code null}.
     */
    List<Proxy> getProxies();

    /**
     * Gets the problems that were encountered during the settings decryption.
     *
     * @return The problems that were encountered during the decryption, can be empty but never {@code null}.
     */
    List<SettingsProblem> getProblems();

			succ += metric.Value
		case tierRequestsFailure:
			fail += metric.Value
		}
	}
	if int(succ) != expSuccess {
		t.Fatalf("Expected %d successes but got %f", expSuccess, succ)
	}
	if int(fail) != expFailure {
		t.Fatalf("Expected %d failures but got %f", expFailure, fail)
	}

// Available returns how many bytes are unused in the buffer.
func (b *Buffer) Available() int { return cap(b.buf) - len(b.buf) }

// Truncate discards all but the first n unread bytes from the buffer
// but continues to use the same allocated storage.
// It panics if n is negative or greater than the length of the buffer.
func (b *Buffer) Truncate(n int) {
	if n == 0 {
		b.Reset()
		return
	}

      // But theoretically we could see sneaky checked exception
      sneakyThrow(exception);
    }
  }

  /**
   * Returns a {@link Stream} containing the elements of the first stream, followed by the elements
   * of the second stream, and so on.
   *
   * <p>This is equivalent to {@code Stream.of(streams).flatMap(stream -> stream)}, but the returned
   * stream may perform better.
   *

{* ../../docs_src/behind_a_proxy/tutorial001_01_py39.py hl[6] *}

If the client tries to go to `/items`, by default, it would be redirected to `/items/`.

But before setting the *CLI Option* `--forwarded-allow-ips` it could redirect to `http://localhost:8000/items/`.

But maybe your application is hosted at `https://mysuperapp.com`, and the redirection should be to `https://mysuperapp.com/items/`.

///

## OpenAPI and API docs { #openapi-and-api-docs }

If you return additional status codes and responses directly, they won't be included in the OpenAPI schema (the API docs), because FastAPI doesn't have a way to know beforehand what you are going to return.

        - label: I already checked if it is not related to FastAPI but to [Pydantic](https://github.com/pydantic/pydantic).
          required: true
        - label: I already checked if it is not related to FastAPI but to [Swagger UI](https://github.com/swagger-api/swagger-ui).
          required: true
        - label: I already checked if it is not related to FastAPI but to [ReDoc](https://github.com/Redocly/redoc).
          required: true