hmac-auth

Summary

• Summary
• Name
• Attributes
• How To Enable
• Test Plugin
  • generate signature:
  • Request body checking
  • Use the generated signature to try the request
• Custom header key
  • Enable request body checking
• Disable Plugin
• Generate Signature Examples

Name

hmac-auth is an authentication plugin that need to work with consumer. Add HMAC Authentication to a service or route.

The consumer then adds its key to request header to verify its request.

Attributes

Name	Type	Requirement	Default	Valid	Description
access_key	string	required			Different consumer objects should have different values, and it should be unique. If different consumers use the same access_key, a request matching exception will occur.
secret_key	string	required			Use as a pair with access_key.
algorithm	string	optional	"hmac-sha256"	["hmac-sha1", "hmac-sha256", "hmac-sha512"]	Encryption algorithm.
clock_skew	integer	optional	0		The clock skew allowed by the signature in seconds. For example, if the time is allowed to skew by 10 seconds, then it should be set to 10. especially, 0 means not checking Date
signed_headers	array[string]	optional			Restrict the headers that are added to the encrypted calculation. After the specified, the client request can only specify the headers within this range. When this item is empty, all the headers specified by the client request will be added to the encrypted calculation
keep_headers	boolean	optional	false	[ true, false ]	Whether it is necessary to keep the request headers of X-HMAC-SIGNATURE, X-HMAC-ALGORITHM and X-HMAC-SIGNED-HEADERS in the http request after successful authentication. true: means to keep the http request header, false: means to remove the http request header.
encode_uri_params	boolean	optional	true	[ true, false ]	Whether to encode the uri parameter in the signature, for example: params1=hello%2Cworld is encoded, params2=hello,world is not encoded. true: means to encode the uri parameter in the signature, false: not to encode the uri parameter in the signature.
validate_request_body	boolean	optional	false	[ true, false ]	Whether to check request body.
max_req_body	integer	optional	512 * 1024		Max allowed body size.

How To Enable

1. set a consumer and config the value of the hmac-auth option

curl http://127.0.0.1:9080/apisix/admin/consumers -H 'X-API-KEY: edd1c9f034335f136f87ad84b625c8f1' -X PUT -d '
{
    "username": "jack",
    "plugins": {
        "hmac-auth": {
            "access_key": "user-key",
            "secret_key": "my-secret-key",
            "clock_skew": 0,
            "signed_headers": ["User-Agent", "Accept-Language", "x-custom-a"]
        }
    }
}'

The default keep_headers is false and encode_uri_params is true.

You can visit the dashboard to complete the above operations through the web interface, first add a consumer:

Then add the hmac-auth plugin to the consumer page:

2. add a Route or add a Service, and enable the hmac-auth plugin

curl http://127.0.0.1:9080/apisix/admin/routes/1 -H 'X-API-KEY: edd1c9f034335f136f87ad84b625c8f1' -X PUT -d '
{
    "uri": "/index.html",
    "plugins": {
        "hmac-auth": {}
    },
    "upstream": {
        "type": "roundrobin",
        "nodes": {
            "127.0.0.1:1980": 1
        }
    }
}'

Test Plugin

generate signature:

The calculation formula of the signature is signature = HMAC-SHAx-HEX(secret_key, signing_string). From the formula, it can be seen that in order to obtain the signature, two parameters, SECRET_KEY and signing_STRING, are required. Where secret_key is configured by the corresponding consumer, the calculation formula of signing_string is signing_string = HTTP Method + \n + HTTP URI + \n + canonical_query_string + \n + access_key + \n + Date + \n + signed_headers_string. If one of the items in signing_string does not exist, you also need to use an empty string instead.

1. HTTP Method : Refers to the GET, PUT, POST and other request methods defined in the HTTP protocol, and must be in all uppercase.
2. HTTP URI : HTTP URI requirements must start with "/", those that do not start with "/" need to be added, and the empty path is "/".
3. Date : Date in http header(GMT format).
4. canonical_query_string :canonical_query_string is the result of encoding the query in the URL (query is the string "key1 = valve1 & key2 = valve2" after the "?" in the URL).
5. signed_headers_string :signed_headers_string is the result of obtaining the fields specified by the client from the request header and concatenating the strings in order.

The coding steps of canonical_query_string are as follows:

• Extract the query item in the URL, that is, the string "key1 = valve1 & key2 = valve2" after the "?" in the URL.
• Split the query into several items according to the & separator, each item is in the form of key=value or only key.
• According to whether the uri parameter is encoded, there are two situations:
• When encode_uri_params is true:
  • Encoding each item after disassembly is divided into the following two situations.
  • When the item has only key, the conversion formula is uri_encode(key) + "=".
  • When the item is in the form of key=value, the conversion formula is in the form of uri_encode(key) + "=" + uri_encode(value). Here value can be an empty string.
  • After converting each item, sort by key in lexicographic order (ASCII code from small to large), and connect them with the & symbol to generate the corresponding canonical_query_string.
• When encode_uri_params is false:
  • Encoding each item after disassembly is divided into the following two situations.
  • When the item has only key, the conversion formula is key + "=".
  • When the item is in the form of key=value, the conversion formula is in the form of key + "=" + value. Here value can be an empty string.
  • After converting each item, sort by key in lexicographic order (ASCII code from small to large), and connect them with the & symbol to generate the corresponding canonical_query_string.

The signed_headers_string generation steps are as follows:

• Obtain the headers specified to be added to the calculation from the request header. For details, please refer to the placement of SIGNED_HEADERS in the next section Use the generated signature to make a request attempt.
• Take out the headers specified by SIGNED_HEADERS in order from the request header, and splice them together in order of name:value. After splicing, a signed_headers_string is generated.

HeaderKey1 + ":" + HeaderValue1 + "\n"\+
HeaderKey2 + ":" + HeaderValue2 + "\n"\+
...
HeaderKeyN + ":" + HeaderValueN + "\n"

Signature string splicing example

Take the following request as an example:

$ curl -i http://127.0.0.1:9080/index.html?name=james&age=36 \
-H "X-HMAC-SIGNED-HEADERS: User-Agent;x-custom-a" \
-H "x-custom-a: test" \
-H "User-Agent: curl/7.29.0"

The signing_string generated according to the signature generation formula is:

"GET
/index.html
age=36&name=james
user-key
Tue, 19 Jan 2021 11:33:20 GMT
User-Agent:curl/7.29.0
x-custom-a:test
"

Note: The last request header also needs + \n.

Generate Signature

Use Python to generate the signature SIGNATURE:

import base64
import hashlib
import hmac

secret = bytes('my-secret-key', 'utf-8')
message = bytes("""GET
/index.html
age=36&name=james
user-key
Tue, 19 Jan 2021 11:33:20 GMT
User-Agent:curl/7.29.0
x-custom-a:test
""", 'utf-8')

hash = hmac.new(secret, message, hashlib.sha256)

# to lowercase base64
print(base64.b64encode(hash.digest()))

Type	Hash
SIGNATURE	8XV1GB7Tq23OJcoz6wjqTs4ZLxr9DiLoY4PxzScWGYg=

Request body checking

When validate_request_body is assigned to true, the plugin will check the request body. The plugin will calculate the hmac-sha value of the request body，and check against the X-HMAC-DIGEST header.

X-HMAC-DIGEST: base64(hmac-sha(<body>))

When there is no request body, you can set X-HMAC-DIGEST value to the hmac-sha of empty string.

Note: The plugin will load the request body to memory to calculate the digest of the request body, which might cause high memory consumption with large bodies. You can limit the max allowed body size by the configuration of max_req_body(default=512KB), request body larger than that will be rejected.

Use the generated signature to try the request

$ curl -i "http://127.0.0.1:9080/index.html?name=james&age=36" \
-H "X-HMAC-SIGNATURE: 8XV1GB7Tq23OJcoz6wjqTs4ZLxr9DiLoY4PxzScWGYg=" \
-H "X-HMAC-ALGORITHM: hmac-sha256" \
-H "X-HMAC-ACCESS-KEY: user-key" \
-H "Date: Tue, 19 Jan 2021 11:33:20 GMT" \
-H "X-HMAC-SIGNED-HEADERS: User-Agent;x-custom-a" \
-H "x-custom-a: test" \
-H "User-Agent: curl/7.29.0"

HTTP/1.1 200 OK
Content-Type: text/html; charset=utf-8
Transfer-Encoding: chunked
Connection: keep-alive
Date: Tue, 19 Jan 2021 11:33:20 GMT
Server: APISIX/2.2
......

Below are two assembly forms of signature information

• The signature information is put together in the request header Authorization field:

$ curl http://127.0.0.1:9080/index.html -H 'Authorization: hmac-auth-v1# + ACCESS_KEY + # + base64_encode(SIGNATURE) + # + ALGORITHM + # + DATE + # + SIGNED_HEADERS' -i
HTTP/1.1 200 OK
Content-Type: text/html
Content-Length: 13175
...
Accept-Ranges: bytes

<!DOCTYPE html>
<html lang="cn">
...

• The signature information is separately placed in the request header:

$ curl http://127.0.0.1:9080/index.html -H 'X-HMAC-SIGNATURE: base64_encode(SIGNATURE)' -H 'X-HMAC-ALGORITHM: ALGORITHM' -H 'Date: DATE' -H 'X-HMAC-ACCESS-KEY: ACCESS_KEY' -H 'X-HMAC-SIGNED-HEADERS: SIGNED_HEADERS' -i
HTTP/1.1 200 OK
Content-Type: text/html
Content-Length: 13175
...
Accept-Ranges: bytes

<!DOCTYPE html>
<html lang="cn">

Note:

1. ACCESS_KEY, SIGNATURE, ALGORITHM, DATE, SIGNED_HEADERS respectively represent the corresponding variables
2. SIGNED_HEADERS is the headers specified by the client to join the encryption calculation. If there are multiple headers, they must be separated by ";": x-custom-header-a;x-custom-header-b
3. SIGNATURE needs to use base64 for encryption: base64_encode(SIGNATURE)

Custom header key

We can customize header key for auth parameters by adding the attribute configuration of the plugin under plugin_attr in conf / config.yaml.

plugin_attr:
  hmac-auth:
    signature_key: X-APISIX-HMAC-SIGNATURE
    algorithm_key: X-APISIX-HMAC-ALGORITHM
    date_key: X-APISIX-DATE
    access_key: X-APISIX-HMAC-ACCESS-KEY
    signed_headers_key: X-APISIX-HMAC-SIGNED-HEADERS
    body_digest_key: X-APISIX-HMAC-BODY-DIGEST

After customizing the header, request example:

$ curl http://127.0.0.1:9080/index.html -H 'X-APISIX-HMAC-SIGNATURE: base64_encode(SIGNATURE)' -H 'X-APISIX-HMAC-ALGORITHM: ALGORITHM' -H 'X-APISIX-DATE: DATE' -H 'X-APISIX-HMAC-ACCESS-KEY: ACCESS_KEY' -H 'X-APISIX-HMAC-SIGNED-HEADERS: SIGNED_HEADERS' -H 'X-APISIX-HMAC-BODY-DIGEST: BODY_DIGEST' -i
HTTP/1.1 200 OK
Content-Type: text/html
Content-Length: 13175
...
Accept-Ranges: bytes

<!DOCTYPE html>
<html lang="cn">

Enable request body checking

$ curl -X "POST" "http://localhost:9080/index.html?age=36&name=james" \
     -H 'X-HMAC-ACCESS-KEY: my-access-key' \
     -H 'X-HMAC-SIGNATURE: lSWO4vcyVoZG5bn8miHudzABAeJQd8tqEHyM7RsjeiU=' \
     -H 'X-HMAC-ALGORITHM: hmac-sha256' \
     -H 'Date: Tue, 24 Aug 2021 03:19:21 GMT' \
     -H 'X-HMAC-SIGNED-HEADERS: User-Agent;X-HMAC-DIGEST' \
     -H 'User-Agent: curl/7.29.0' \
     -H 'X-HMAC-DIGEST: L9b/+QMvhvnoUlSw5vq+kHPqnZiHGl61T8oavMVTaC4=' \
     -H 'Content-Type: text/plain; charset=utf-8' \
     -d "{\"hello\":\"world\"}"

HTTP/1.1 200 OK
Content-Type: text/html; charset=utf-8
Transfer-Encoding: chunked
Connection: keep-alive
Date: Tue, 14 Sep 2021 03:28:14 GMT
Server: APISIX/2.9
...

Disable Plugin

When you want to disable the hmac-auth plugin, it is very simple, you can delete the corresponding json configuration in the plugin configuration, no need to restart the service, it will take effect immediately:

$ curl http://127.0.0.1:9080/apisix/admin/routes/1 -H 'X-API-KEY: edd1c9f034335f136f87ad84b625c8f1' -X PUT -d '
{
    "uri": "/index.html",
    "plugins": {},
    "upstream": {
        "type": "roundrobin",
        "nodes": {
            "127.0.0.1:1980": 1
        }
    }
}'

Generate Signature Examples

Take HMAC SHA256 as an example to introduce the signature generation examples in different languages. Need to pay attention to the handling of newline characters in signature strings in various languages, which can easily lead to the problem of {"message":"Invalid signature"}.

Example inputs:

Variable	Value
secret	the shared secret key here
message	this is signature string

Example outputs:

Type	Hash
hexit	ad1b76c7e5054009380edca35d3f36cc5b6f45c82ee02ea3af64197ebddb9345
base64	rRt2x+UFQAk4DtyjXT82zFtvRcgu4C6jr2QZfr3bk0U=

Please refer to HMAC Generate Signature Examples