Include a V4 signature in a URL (recommended) - Object Storage Service

In addition to using the HTTP Authorization header for providing authentication information, you can use query string parameters to authenticate requests when you want to use a URL to express a request. This way, you can grant users temporary access permissions on the specified Object Storage Service (OSS) resources without exposing your access credentials. This topic describes how to include a V4 signature in a URL.

Use OSS SDKs to automatically implement V4 signatures

OSS SDKs support the automatic implementation of V4 signatures. We recommend that you use OSS SDKs to initiate requests. This eliminates the need to manually calculate signatures. For more information about how to sign requests by using the V4 signature algorithm when you use OSS SDKs for different programming languages, see the sample code of OSS SDKs. The following table provides references to the sample code used to sign requests by using the V1 signature algorithm when you use OSS SDKs for different programming languages.

SDK	Example	Sample code
Java	Initialization	OSSV4Signer.java
PHP	Initialization	SignerV4.php
Node.js	Initialization	signatureUrlV4.js
Browser.js	Initialization	signatureUrlV4.js
Python	Initialization	auth.py
Go	Initialization	v4.go
C++	Initialization	SignerV4.cc
C	Initialization	oss_auth.c

URL signing

Example

https://examplebucket.oss-cn-hangzhou.aliyuncs.com/exampleobject?x-oss-signature-version=OSS4-HMAC-SHA256&x-oss-credential=<AccessKeyId>/20231203/cn-hangzhou/oss/aliyun_v4_request&x-oss-date=20231203T121212Z&x-oss-expires=86400&x-oss-additional-headers=host&x-oss-signature=<signature-to-be-calculated>

For readability, the fields in the x-oss-credential parameter in the preceding URL are separated by forward slashes (/). When you initiate a request, URI-encode the forward slashes (/) in the URL to convert them into %2F. Example:

&x-oss-credential=<AccessKeyId>%2F20231203%2Fcn-hangzhou%2Foss%2Faliyun_v4_request

Query string parameters

Parameter	Type	Required	Example	Description
x-oss-signature-version	String	Yes	OSS4-HMAC-SHA256	The version and algorithm of the signature. Set the value to OSS4-HMAC-SHA256.
x-oss-credential	String	Yes	LTAI********************/20231203/cn-hangzhou/oss/aliyun_v4_request	The credentials that you can use to calculate the signature. Format: `<AccessKeyId>/<date>/<region>/oss/aliyun_v4_request` AccessKeyId: the AccessKey ID in the AccessKey pair. date: the date when the request was initiated. region: the region in which the requested resource resides. oss: the name of the requested service. Valid value: oss. aliyun_v4_request: the description of the signature version in the request. Valid value: aliyun_v4_request.
x-oss-date	String	Yes	20231203T121212Z	The time when the URL was signed. The time follows the ISO 8601 standard. To avoid time differences, an offset of 15 minutes after the URL was signed is allowed. Note The time is used as the timestamp for the string to sign. The value must be the same as that of the date field in the derived signing key.
x-oss-expires	Integer	Yes	3600	The validity period of the signed URL. Unit: seconds. Minimum value: 1. Maximum value: 604800.
x-oss-additional-headers	String	No	host	The headers that you want to add to calculate the signature. We recommend that you sign all request headers that you want to include in your request. The following items describe the requirements for constructing the parameter: All headers in the x-oss-additional-headers parameter must be in lowercase letters. All headers in the x-oss-additional-headers parameter must be sorted in alphabetical order. All headers in an array are separated by semicolons (;) to obtain a string.
x-oss-signature	String	Yes	77Dv****************	The description of the signature verification. The x-oss-signature parameter is not included in the signature calculation.
x-oss-security-token	String	No	CAIS********************************	The security token issued by Security Token Service (STS). This parameter is required only when you use an STS user to construct a signature for the URL.

Signature calculation process

The method used to calculate a signature for a URL is similar to the method used to calculate a signature for the Authorization header. The following items describe the differences between the two methods:

The x-oss-content-sha256 header that describes a payload hash is not used to calculate a signature for a URL. When you create a signed URL, you cannot evaluate the payload content. Instead, UNSIGNED-PAYLOAD is used.
If a key in the query string parameters of a signed URL is the same as a header to be signed but their values are different, an error is reported. If a key has multiple values, all values of the key are compared at the same time. If the values are different, an error is reported.
If you use the access credentials obtained from STS to access OSS resources in a signed URL, you must add the x-oss-security-token parameter to the query string of the URL.
The x-oss-signature parameter in the query string is not included in the signature calculation.

Step 1: Create a canonical request

Convert the content of your request to the canonical format.

Format

HTTP Verb + "\n" +
Canonical URI + "\n" +
Canonical Query String + "\n" +
Canonical Headers + "\n" +
Additional Headers + "\n" +
Hashed PayLoad

The following table describes the preceding parameters.

Parameter	Type	Required	Example value	Description
HTTP Verb	Enumeration	Yes	PUT	The HTTP method, which can be PUT, GET, POST, HEAD, DELETE, or OPTIONS.
Canonical URI	String	Yes	/examplebucket/exampleobject	A URI-encoded string. Do not encode the forward slash (/) in the absolute path. The URI starts with a forward slash (`/`) that follows the domain name up to the end of the string if query string parameters are not included. The URI starts with a forward slash (`/`) that follows the domain name and ends with a question mark (?) if query string parameters are included. The following items describe how to specify a canonical URI based on the resources included in the request URI: If the request URI contains both a bucket name and an object name, the canonical URI is in the following format: `/examplebucket/exampleobject`. If the request URI contains only a bucket name, the canonical URI is in the following format: `/examplebucket/`. If the request URI contains only an object name, the canonical URI is set to `/`.
Canonical Query String	String	Yes	UriEncode("marker") + "=" + UriEncode("someMarker") + "&" + UriEncode("max-keys") + "=" + UriEncode("20") + "&" + UriEncode("prefix") + "=" + UriEncode("somePrefix")	The URI-encoded query string parameters. You must URI-encode each key and value individually. Sort the parameters in the canonical query string in alphabetical order by key name after you encode the parameters. If identical keys exist, sort the keys in chronological order based on the time when they were added. If a key does not have a value, add only the key. If a request does not include a query string, set the canonical query string to an empty string (`""`). You must add a line feed at the end. If a key in the query string parameters of a signed URL is the same as a header to be signed, but their values are different, an error is reported. If a key has multiple values, all values of the key are compared at the same time. If the values are different, an error is reported.
Canonical Headers	String	Yes	`host:cname.com x-oss-content-sha256:e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855 x-oss-date:20231203T121212Z`	A string obtained by converting the list of request headers to the canonical format. Add a line feed at the end of the string. A header key and value are separated by a colon (`:`), and headers are separated by a line feed. Header keys must be in lowercase and sorted in alphabetical order. Leading or trailing spaces in header values must be trimmed. Header keys are sorted in alphabetical order. The request time is specified by the `x-oss-date` header. The time follows the ISO 8601 standard and is displayed in UTC. Example: 20231203T121212Z. The `x-oss-content-sha256` header that describes a payload hash is not used to calculate a signature for a URL. When you create a signed URL, you cannot evaluate the payload content. Instead, UNSIGNED-PAYLOAD is used. Canonical Headers must include the following types: The headers specified by Additional Headers and used for signature calculation Headers that must be added to Canonical Headers if they are in the request: Content-Type Content-MD5 x-oss-*
Additional Headers	String	Yes	content-length;host	The headers to be added to calculate the signature. All headers must be in lowercase and sorted in alphabetical order.
Hashed PayLoad	String	Yes	UNSIGNED-PAYLOAD	Valid value: UNSIGNED-PAYLOAD.

Example

"GET" | "PUT" | ... + "\n" +
UriEncode(<Resource>) + "\n" +
UriEncode(<QueryParam1>) + "=" + UriEncode(<Value>) + "&" + UriEncode(<QueryParam2>) + "\n" +
Lowercase(<HeaderName1>) + ":" + Trim(<value>) + "\n" + Lowercase(<HeaderName2>) + ":" + Trim(<value>) + "\n" + "\n"
Lowercase(<AdditionalHeaderName1>) + ";" + Lowercase(<AdditionalHeaderName2>) + "\n" +
UNSIGNED-PAYLOAD

Step 2: Create a string to sign

Concatenate the following strings to create a string to sign.

Format

"OSS4-HMAC-SHA256" + "\n" +
TimeStamp + "\n" +
Scope + "\n" +
Hex(SHA256Hash(<CanonicalRequest>))

The following table describes the preceding parameters.

Parameter	Type	Required	Example value	Description
OSS4-HMAC-SHA256	Enumeration	Yes	OSS4-HMAC-SHA25	The algorithm used to create the hash of the canonical request. Set the value to OSS4-HMAC-SHA256.
TimeStamp	String	Yes	20231203T121212Z	The current time in UTC. The time must follow the ISO 8601 standard.
Scope	String	Yes	20231203/cn-hangzhou/oss/aliyun_v4_request	The scope information. This restricts the calculated signature to the specified region and service. Format: `<SignDate>/<Region>/oss/aliyun_v4_request` SignDate: the date when the request is initiated. Region: the region in which the requested resource resides. oss: the name of the requested service. Valid value: oss. aliyun_v4_request: the description of the signature version in the request. Valid value: aliyun_v4_request.
CanonicalRequest	String	Yes	PUT /examplebucket/exampleobject x-oss-additional-headers=host&x-oss-credential=accesskeyid%2F20231203%2Fcn-hangzhou%2Foss%2Faliyun_v4_request&x-oss-date=20231203T121212Z&x-oss-expires=86400&x-oss-signature-version=OSS4-HMAC-SHA256 host:examplebucket.oss-cn-hangzhou.aliyuncs.com x-oss-meta-author:alice x-oss-meta-magic:abracadabra host UNSIGNED-PAYLOAD	The string created in Step 1.

Example

"OSS4-HMAC-SHA256" + "\n" +
FormatISO8601 + "\n" +
20231203/cn-hangzhou/oss/aliyun_v4_request + "\n" +
Hex(SHA256Hash(<CanonicalRequest>))

Step 3: Calculate the signature

Create a signing key and use the signing key to calculate the signature.

Calculate the signing key.

HMAC-SHA256(HMAC-SHA256(HMAC-SHA256(HMAC-SHA256("aliyun_v4" + SK, Date), Region), "oss"), "aliyun_v4_request");

Calculate the signature.

HEX(HMAC-SHA256(SigningKey, StringToSign))

Signature calculation example

In this example, a signed URL is created. You can share the signed URL to third-party users to allow the users to upload data to OSS. The following section describes how to include a V4 signature in the URL.

Parameters
Parameter
Example
AccessKeyId
accesskeyid
AccessKeySecret
accesskeysecret
Timestamp
20231203T121212Z
Bucket
examplebucket
Object
exampleobject
Region
cn-hangzhou

PutObject

https://examplebucket.oss-cn-hangzhou.aliyuncs.com/exampleobject?x-oss-signature-version=OSS4-HMAC-SHA256&x-oss-credential=accesskeyid/20231203/cn-hangzhou/oss/aliyun_v4_request&x-oss-date=20231203T121212Z&x-oss-expires=86400&x-oss-additional-headers=host&x-oss-signature=<signature-to-be-calculated>
Host: examplebucket.oss-cn-hangzhou.aliyuncs.com
x-oss-meta-author: alice
x-oss-meta-magic: abracadabra

To include a V4 signature in a URL, perform the following steps:

Create a canonical request.

PUT
/examplebucket/exampleobject
x-oss-additional-headers=host&x-oss-credential=accesskeyid%2F20231203%2Fcn-hangzhou%2Foss%2Faliyun_v4_request&x-oss-date=20231203T121212Z&x-oss-expires=86400&x-oss-signature-version=OSS4-HMAC-SHA256
host:examplebucket.oss-cn-hangzhou.aliyuncs.com
x-oss-meta-author:alice
x-oss-meta-magic:abracadabra

host
UNSIGNED-PAYLOAD

Create a string to sign.

OSS4-HMAC-SHA256
20231203T121212Z
20231203/cn-hangzhou/oss/aliyun_v4_request
672d815902f04dd8aa90a558931f471cc7269d08a122a5e9028022d9f723332c

Calculate the signature.
1. Calculate the signing key.
  Note
  For readability, the following example describes the Base64-encoded value of the signing key.
```
WVjaYR8lCj9YC5PUS2RSZQANYbuh9DhMFxjU1NtZKfc=
```
2. Calculate the signature.
```
2c6c9f10d8950fb150290ef6f42570e33cd45d6a57ec7887de75fa2ec45b4c72
```

Add the signature to the URL.

https://examplebucket.oss-cn-hangzhou.aliyuncs.com?x-oss-additional-headers=host&x-oss-credential=accesskeyid%2F20231203%2Fcn-hangzhou%2Foss%2Faliyun_v4_request&x-oss-date=20231203T121212Z&x-oss-expires=86400&x-oss-signature=2c6c9f10d8950fb150290ef6f42570e33cd45d6a57ec7887de75fa2ec45b4c72&x-oss-signature-version=OSS4-HMAC-SHA256
Host: examplebucket.oss-cn-hangzhou.aliyuncs.com
x-oss-meta-author: alice
x-oss-meta-magic: abracadabra

Complete sample code for signature calculation

The parameters provided in the preceding signature calculation example are used to describes the complete process of signature calculation by using OSS SDK for Java.

import com.aliyun.oss.common.utils.BinaryUtil;
import org.apache.commons.codec.digest.DigestUtils;
import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
import java.net.URL;

public class Demo {

    /**
     * Signature calculation tool
     *
     * @return url
     */
    public static void main(String[] args) throws Exception {
        // Before you run the sample code, make sure that the OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET environment variables are configured. 
        String accesskeyid =  System.getenv().get("OSS_ACCESS_KEY_ID");
        String accesskeysecret =  System.getenv().get("OSS_ACCESS_KEY_SECRET");
        // Step 1: Create a canonical request. 
        String canonicalRequest =
                "PUT\n" +
                        "/examplebucket/exampleobject\n" +
                        "x-oss-additional-headers=host&x-oss-credential="+accesskeyid+"%2F20231203%2Fcn-hangzhou%2Foss%2Faliyun_v4_request&x-oss-date=20231203T121212Z&x-oss-expires=86400&x-oss-signature-version=OSS4-HMAC-SHA256\n" +
                        "host:examplebucket.oss-cn-hangzhou.aliyuncs.com\n" +
                        "x-oss-meta-author:alice\n" +
                        "x-oss-meta-magic:abracadabra\n" +
                        "\n" +
                        "host\n" +
                        "UNSIGNED-PAYLOAD";

        // Step 2: Create a string to sign. 
        String stringToSign = "OSS4-HMAC-SHA256\n" +
                "20231203T121212Z\n" +
                "20231203/cn-hangzhou/oss/aliyun_v4_request\n" +
                DigestUtils.sha256Hex(canonicalRequest);

        // Step 3: Calculate the signature. 
        byte[] dateKey = hmacsha256(("aliyun_v4" + accesskeysecret).getBytes(), "20231203");
        byte[] dateRegionKey = hmacsha256(dateKey, "cn-hangzhou");
        byte[] dateRegionServiceKey = hmacsha256(dateRegionKey, "oss");
        byte[] signingKey = hmacsha256(dateRegionServiceKey, "aliyun_v4_request");

        byte[] result = hmacsha256(signingKey, stringToSign);
        String signature = BinaryUtil.toHex(result);
        System.out.println("signature:" + signature);

        // Step 4: Add the signature to the URL. 
        String resourcePath = "exampleobject";
        String endpoint = "https://examplebucket.oss-cn-hangzhou.aliyuncs.com";
        String queryString = "x-oss-additional-headers=host&" +
                "x-oss-credential="+accesskeyid+"%2F20231203%2Fcn-hangzhou%2Foss%2Faliyun_v4_request&" +
                "x-oss-date=20231203T121212Z&" +
                "x-oss-expires=86400&" +
                "x-oss-signature=" + signature + "&" +
                "x-oss-signature-version=OSS4-HMAC-SHA256";

        String urlStr = endpoint + "/" + resourcePath + "?" + queryString;
        URL url = new URL(urlStr);
        System.out.println("url:" + url);
    }

    public static byte[] hmacsha256(byte[] key, String data) {
        try {
            // Initialize the HMAC key specification, set the algorithm to HMAC-SHA256, and use the provided key. 
            SecretKeySpec secretKeySpec = new SecretKeySpec(key, "HmacSHA256");

            // Obtain a Mac instance and use the getInstance method to set the algorithm to HMAC-SHA256. 
            Mac mac = Mac.getInstance("HmacSHA256");
            // Use the key to initialize the Mac instance. 
            mac.init(secretKeySpec);

            // Calculate the HMAC value. Use the doFinal method to receive the data to be calculated and return the calculation results in arrays. 
            byte[] hmacBytes = mac.doFinal(data.getBytes());

            return hmacBytes;
        } catch (Exception e) {
            throw new RuntimeException("Failed to calculate HMAC-SHA256", e);
        }
    }
}

Sample output:

signature:2c6c9f10d8950fb150290ef6f42570e33cd45d6a57ec7887de75fa2ec45b4c72
url:https://examplebucket.oss-cn-hangzhou.aliyuncs.com/exampleobject?x-oss-additional-headers=host&x-oss-credential=accesskeyid%2F20231203%2Fcn-hangzhou%2Foss%2Faliyun_v4_request&x-oss-date=20231203T121212Z&x-oss-expires=86400&x-oss-signature=2c6c9f10d8950fb150290ef6f42570e33cd45d6a57ec7887de75fa2ec45b4c72&x-oss-signature-version=OSS4-HMAC-SHA256

Parameter	Example
AccessKeyId	accesskeyid
AccessKeySecret	accesskeysecret
Timestamp	20231203T121212Z
Bucket	examplebucket
Object	exampleobject
Region	cn-hangzhou