}

    /**
     * Gets a typed value from a document map with a default value.
     *
     * @param <T> the type to convert the value to
     * @param doc the document map to extract the value from
     * @param key the key to look up in the document map
     * @param clazz the class type to convert the value to
     * @param defaultValue the default value to return if the key is not found or conversion fails

There's a whole chapter here in the documentation about it, you can read it at [Additional Responses in OpenAPI](additional-responses.md){.internal-link target=_blank}.

## OpenAPI Extra { #openapi-extra }

When you declare a *path operation* in your application, **FastAPI** automatically generates the relevant metadata about that *path operation* to be included in the OpenAPI schema.

/// note | Technical details

        return logger;
    }

    /**
     * Gets the appropriate extractor for the given response data.
     * Selects an extractor based on the MIME type of the file.
     *
     * @param responseData the response data containing the file to extract
     * @return the extractor instance for processing the file
     * @throws FessSystemException if no suitable extractor factory can be found
     */
    @Override

	if err != ErrNone {
		return err
	}

	// Extract all the signed headers along with its values.
	extractedSignedHeaders, errCode := extractSignedHeaders(signV4Values.SignedHeaders, r)
	if errCode != ErrNone {
		return errCode
	}

	cred, _, s3Err := checkKeyValid(r, signV4Values.Credential.accessKey)
	if s3Err != ErrNone {
		return s3Err
	}

	// Extract date, if not present throw error.
	var date string

     * @param outExt the output file extension
     * @return the extracted text content
     * @throws ExtractException if an error occurs while reading the file
     */
    protected String getOutputContent(final File outputFile, final String outExt) {
        final Extractor extractor = getExtractor(outExt);
        if (extractor != null) {
            final Map<String, String> params = new HashMap<>();

            op.setRefreshPolicy(Constants.TRUE);
        });
        return failureUrl;
    }

    /**
     * Extracts and returns the stack trace from a throwable as a string.
     * The stack trace is abbreviated if it exceeds the configured maximum length.
     *
     * @param t the throwable to extract the stack trace from
     * @return the stack trace as a string, or empty string if extraction fails
     */

* `username`: `Rick`
* `password`: `Portal Gun`
* `extra`: `Mr. Poopybutthole`

They will receive an error response telling them that the field `extra` is not allowed:

```json
{
    "detail": [
        {
            "type": "extra_forbidden",
            "loc": ["body", "extra"],
            "msg": "Extra inputs are not permitted",
            "input": "Mr. Poopybutthole"
        }
    ]
}
```

 * certificate.
 *
 * Use of the chain cleaner is necessary to omit unexpected certificates that aren't relevant to
 * the TLS handshake and to extract the trusted CA certificate for the benefit of certificate
 * pinning.
 */
abstract class CertificateChainCleaner {
  @Throws(SSLPeerUnverifiedException::class)
  abstract fun clean(
    chain: List<Certificate>,

        """
        elt = self.element.find('sts:{}'.format(name), _STS_NS)
        return STSElement(self.root_name, elt) if elt is not None else None

    def get_child_text(self, name, strict=True):
        """Extract text of a child element. If strict, and child element is
        not present, raises InvalidXMLError and otherwise returns
        None.

        """
        if strict:
            try:

**FastAPI** will **extract** the data for **each field** from the **headers** in the request and give you the Pydantic model you defined.

## Check the Docs { #check-the-docs }

You can see the required headers in the docs UI at `/docs`:

<div class="screenshot">
<img src="/img/tutorial/header-param-models/image01.png">
</div>

## Forbid Extra Headers { #forbid-extra-headers }