But let's save you the time of reading the full long specification just to find those little pieces of information you need.

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`:

/*
 * Copyright (C) 2025 Block, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,

	// Wait for the server to send the first response.
	<-serverSent

	// Read back from the stream and block.
	nowBlocking := make(chan struct{})
	stopBlocking := make(chan struct{})
	defer close(stopBlocking)
	go func() {
		st.Results(func(b []byte) error {
			close(nowBlocking)
			// Block until test is done.
			<-stopBlocking
			return nil
		})
	}()

	<-nowBlocking

/*
 * Copyright (C) 2024 Block, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,

								<la:link
									href="/search?q=${f:u(item)}${fe:facetQuery()}${fe:geoQuery()}">${f:h(item)}</la:link>
							</c:if>
							<c:if test="${3 <= s.index}">
								<la:link styleClass="d-none d-sm-inline-block"
									href="/search?q=${f:u(item)}${fe:facetQuery()}${fe:geoQuery()}">${f:h(item)}</la:link>
							</c:if>
						</c:forEach>
					</p>
				</div>
			</div>
		</c:if>

								<la:link
									href="/search?q=${f:u(item)}${fe:facetQuery()}${fe:geoQuery()}">${f:h(item)}</la:link>
							</c:if>
							<c:if test="${3 <= s.index}">
								<la:link styleClass="d-none d-sm-inline-block"
									href="/search?q=${f:u(item)}${fe:facetQuery()}${fe:geoQuery()}">${f:h(item)}</la:link>
							</c:if>
						</c:forEach>
					</p>
				</div>
			</div>
		</c:if>

	if err != nil {
		fmt.Printf("error generating key: %s n", err)
		os.Exit(1)
	}

	// dump private key to file
	privateKeyBytes := x509.MarshalPKCS1PrivateKey(privatekey)
	privateKeyBlock := &pem.Block{
		Type:  "RSA PRIVATE KEY",
		Bytes: privateKeyBytes,
	}
	privatePem, err := os.Create("support_private.pem")
	if err != nil {
		fmt.Printf("error when create private.pem: %s n", err)
		os.Exit(1)
	}

/*
 * Copyright (C) 2025 Block, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,

    line-height: normal;
    font-weight: bold;
}

button.dl {
  font-weight: 300;
  font-size: 25px;
  line-height: 40px;
  padding: 3px 10px;
  display: inline-block;
  border-radius: 6px;
  color: #f0f0f0;
  margin: 5px 0;
  width: auto;
}

.logo {
  text-align: center;
  margin-top: 150px;

package once

// Singleton contains a pointer to T that must be set once.
// Until the value is set all Get() calls will block.
type Singleton[T any] struct {
	v   *T
	set chan struct{}
}

// NewSingleton creates a new unset singleton.
func NewSingleton[T any]() *Singleton[T] {
	return &Singleton[T]{set: make(chan struct{}), v: nil}
}

// Get will return the singleton value.
func (s *Singleton[T]) Get() *T {
	<-s.set
	return s.v