/*
 * 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,

/*
 * Copyright (C) 2022 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,

/*
 * 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,

        - -ST1016
        - -U1000
  exclusions:
    generated: lax
    rules:
      - linters:
          - forcetypeassert
        path: _test\.go
      - path: (.+)\.go$
        text: 'empty-block:'
      - path: (.+)\.go$
        text: 'unused-parameter:'
      - path: (.+)\.go$
        text: 'dot-imports:'
      - path: (.+)\.go$
        text: should have a package comment
      - path: (.+)\.go$

    void testDES() throws Exception {
        // Given
        byte[] key = "testkey1".getBytes(); // 8 bytes for DES
        byte[] plaintext = "12345678".getBytes(); // 8 bytes (DES block size)

        // When
        Cipher desCipher = Crypto.getDES(key);
        desCipher.init(Cipher.ENCRYPT_MODE, new SecretKeySpec(key, "DES"));
        byte[] encrypted = desCipher.doFinal(plaintext);

/*
 * 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,

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) 2022 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,