# Common request headers The following table describes headers that can be used by various types of Amazon S3 REST requests. | Header Name | Description | | --- | --- | | Authorization | The information required for request authentication. For more information, go to [The Authentication Header](https://docs.aws.amazon.com/AmazonS3/latest/userguide/RESTAuthentication.html#ConstructingTheAuthenticationHeader) in the *Amazon Simple Storage Service Developer Guide*. For anonymous requests this header is not required. | | Access-Control-Request-Method | A list of HTTP methods that is sent as a pre-flight CORS request. If the pre-flight CORS evaluation is successful, then the specified methods are allowed to be used in the following CORS request. | | Content-Length | Length of the message (without the headers) according to RFC 2616. This header is required for PUTs and operations that load XML, such as logging and ACLs. | | Content-Type | The content type of the resource in case the request has content in the body. Example: `text/plain` | | Content-MD5 | The base64 encoded 128-bit MD5 digest of the message (without the headers) according to RFC 1864. This header can be used as a message integrity check to verify that the data is the same data that was originally sent. Although it is optional, we recommend using the Content-MD5 mechanism as an end-to-end integrity check. For more information about REST request authentication, go to [REST Authentication](https://docs.aws.amazon.com/AmazonS3/latest/userguide/RESTAuthentication.html?r=1821) in the *Amazon Simple Storage Service Developer Guide*. | | Date | The date that can be used to create the signature contained in the `Authorization` header. If the `Date` header is to be used for signing it must be specified in the ISO 8601 basic format. In this case, the `x-amz-date` header is not needed. Note that when `x-amz-date` is present, it always overrides the value of the `Date` header. If the Date header is not used for signing, it can be one of the full date formats specified by [RFC 2616](http://tools.ietf.org/html/rfc2616#section-3.3), section 3.3. For example, the date/time `Wed, 01 Mar 2006 12:00:00 GMT` is a valid date/time header for use with Amazon S3. If you are using the `Date` header for signing, then it must be in the ISO 8601 basic `YYYYMMDD'T'HHMMSS'Z'` format. If `Date` is specified but is not in ISO 8601 basic format, then you must also include the `x-amz-date` header. If `Date` is specified in ISO 8601 basic format, then this is sufficient for signing requests and you do not need the `x-amz-date` header. For more information, see [Handling Dates in Signature Version 4](https://docs.aws.amazon.com/general/latest/gr/sigv4-date-handling.html) in the *Amazon Web Services Glossary*. | | Expect | When your application uses 100-continue, it does not send the request body until it receives an acknowledgment. If the message is rejected based on the headers, the body of the message is not sent. This header can be used only if you are sending a body. Valid Values: 100-continue | | Host | For path-style requests, the value is `s3.amazonaws.com`. For virtual-style requests, the value is `BucketName.s3.amazonaws.com`. For more information, go to [Virtual Hosting](https://docs.aws.amazon.com/AmazonS3/latest/userguide/VirtualHosting.html) in the *Amazon Simple Storage Service User Guide*. This header is required for HTTP 1.1 (most toolkits add this header automatically); optional for HTTP/1.0 requests. | | Origin | An endpoint that specifies the server name of the initial requester. | | x-amz-content-sha256 | When using signature version 4 to authenticate request, this header provides a hash of the request payload. For more information see [Signature Calculations for the Authorization Header: Transferring Payload in a Single Chunk (AWS Signature Version 4)](sig-v4-header-based-auth.md). When uploading object in chunks, you set the value to `STREAMING-AWS4-HMAC-SHA256-PAYLOAD` to indicate that the signature covers only headers and that there is no payload. For more information, see [Signature Calculations for the Authorization Header: Transferring Payload in Multiple Chunks (Chunked Upload) (AWS Signature Version 4)](sigv4-streaming.md). | | x-amz-date | The date used to create the signature in the Authorization header. The format must be ISO 8601 basic in the `YYYYMMDD'T'HHMMSS'Z'` format. For example, the date/time `20170210T120000Z` is a valid `x-amz-date` for use with Amazon S3. `x-amz-date` is optional for all requests; it can be used to override the date used for signing requests. If the `Date` header is specified in the ISO 8601 basic format, then `x-amz-date` is not needed. When `x-amz-date` is present, it always overrides the value of the `Date` header. For more information, see [Handling Dates in Signature Version 4](https://docs.aws.amazon.com/general/latest/gr/sigv4-date-handling.html) in the *Amazon Web Services Glossary*. | | x-amz-security-token | This header can be used in the following scenarios: [\[See the AWS documentation website for more details\]](http://docs.aws.amazon.com/AmazonS3/latest/API/RESTCommonRequestHeaders.html) This header is required for requests that use Amazon DevPay and requests that are signed by using temporary security credentials. |