For example, if you want to read or manipulate the request body before it is processed by your application.

/// danger

This is an "advanced" feature.

If you are just starting with **FastAPI** you might want to skip this section.

///

## Use cases { #use-cases }

Some use cases include:

* Converting non-JSON request bodies to JSON (e.g. [`msgpack`](https://msgpack.org/index.html)).

        // Validate compression count
        if (compressionCount < 0 || compressionCount > 16) {
            throw new SMBProtocolDecodingException("Invalid compression count: " + compressionCount);
        }

        // Skip padding
        bufferIndex += 2;

        // Read flags
        this.flags = SMBUtil.readInt4(buffer, bufferIndex);
        bufferIndex += 4;

        // Validate remaining buffer size for algorithms

	if err != nil {
		return c, err
	}

	for _, cfgName := range openIDTargets {
		getCfgVal := func(cfgParam string) string {
			// As parameters are already validated, we skip checking
			// if the config param was found.
			val, _, _ := s.ResolveConfigParam(config.IdentityOpenIDSubSys, cfgName, cfgParam, false)
			return val
		}

            // Verify the path is correctly encoded in UTF-16LE
            ByteBuffer bb = ByteBuffer.wrap(dst).order(ByteOrder.LITTLE_ENDIAN);
            bb.getShort(); // Skip referral level

            byte[] pathBytes = path.getBytes(StandardCharsets.UTF_16LE);
            byte[] encodedPath = new byte[pathBytes.length];
            bb.get(encodedPath);

        }

        extension.fixtures.matching(fixtureProject -> fixtureProject.equals(project) == false)
            .all(fixtureProject -> project.evaluationDependsOn(fixtureProject.getPath()));

        // Skip docker compose tasks if it is unavailable
        maybeSkipTasks(tasks, dockerSupport, Test.class);
        maybeSkipTasks(tasks, dockerSupport, getTaskClass("org.elasticsearch.gradle.internal.test.RestIntegTestTask"));

	// SkipDecommissioned set to 'true' if the call requires skipping the pool being decommissioned.
	// mainly set for certain WRITE operations.
	SkipDecommissioned bool
	// SkipRebalancing should be set to 'true' if the call should skip pools
	// participating in a rebalance operation. Typically set for 'write' operations.
	SkipRebalancing bool

            m.ptype = 0;
            m.flags = flag;

            NdrBuffer buf = new NdrBuffer(new byte[1024], 0);
            m.encode(buf);

            // Reset and skip to flags field
            buf.setIndex(3);
            assertEquals(flag, buf.dec_ndr_small());
        }
    }

}

// NewDummyDataGen returns a ReadSeeker over the first `totalLength`
// bytes from the infinite stream consisting of repeated
// concatenations of `alphabets`.
//
// The skipOffset (generally = 0) can be used to skip a given number
// of bytes from the beginning of the infinite stream. This is useful
// to compare such streams of bytes that may be split up, because:
//
// Given the function:
//
//	f := func(r io.Reader) string {

But first, let's check some small concepts.

## In a hurry? { #in-a-hurry }

If you don't care about any of these terms and you just need to add security with authentication based on username and password *right now*, skip to the next chapters.

## OAuth2 { #oauth2 }

OAuth2 is a specification that defines several ways to handle authentication and authorization.

It is quite an extensive specification and covers several complex use cases.

    if (alreadyEncoded &&
      (
        codePoint == '\t'.code ||
          codePoint == '\n'.code ||
          codePoint == '\u000c'.code ||
          codePoint == '\r'.code
      )
    ) {
      // Skip this character.
    } else if (codePoint == ' '.code && encodeSet === FORM_ENCODE_SET) {
      // Encode ' ' as '+'.
      writeUtf8("+")
    } else if (codePoint == '+'.code && plusIsSpace) {