我想使用R包httr通过其API访问EC2服务。但我有点不确定如何开始，因为它不属于"Oauth2.0"的常见身份验证格式，在这种格式中，你有常见的：密钥、秘密、令牌和签名系统。我认为EC2使用了"签名版本2"方法，但我不清楚它是如何工作的。
查看EC2提供的有关在http://docs.amazonwebservices.com/AWSEC2/latest/UserGuide/using-query-api.html
我想我需要签名的价值。。。。但不知道如何获得
我已经尝试使用httr使用一些给定的命令，如下所示。我可以调整URL字符串中的大多数参数来表示我和我想做的事情，例如AWSAccessKeyId、ImageId、endpoint和Action等……但只是不知道从哪里获取签名值。
此外，在给出的一些例子中，他们似乎也没有提供秘密访问密钥。。。
因此，尝试过的命令如下，更改了一些值来表示我，但得到了以下内容：
require(httr)
GET("https://ec2.amazonaws.com/
?Action=RunInstances
&ImageId=ami-60a54009
&MaxCount=3
&MinCount=1
&Placement.AvailabilityZone=us-east-1b
&Monitoring.Enabled=true
&AWSAccessKeyId=0GS7553JW74RRM612K02EXAMPLE
&Version=2012-10-01
&Expires=2010-10-10T12:00:00Z
&Signature=lBP67vCvGlDMBQ1dofZxg8E8SUEXAMPLE
&SignatureVersion=2
&SignatureMethod=HmacSHA256")
我得到的回应是：
Response [http://aws.amazon.com/ec2/]
Status: 200
Content-type: text/html; charset=UTF-8
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<link rel="icon" type="image/ico" href="//d36cz9buwru1tt.cloudfront.net/favicon.ico">
<link rel="shortcut icon" type="image/ico" href="//d36cz9buwru1tt.cloudfront.net/favicon.ico">
<meta name="description" content="Amazon Elastic Compute Cloud delivers scalable, pay-as-you-go compute capacity in the cloud. " /><meta name="keywords" content="" /> ...
有人对EC2api及其身份验证过程有任何经验吗？使用R是否足够容易，以便能够使用我选择的AMI(加载了R和其他相关包)来设置和运行linux实例，然后在这些实例中运行一些R命令，并返回输出？
不要认为它真的与我的会话信息有关，但以防万一：
sessionInfo()
R version 2.15.1 (2012-06-22)
Platform: x86_64-apple-darwin9.8.0/x86_64 (64-bit)
locale:
[1] en_GB.UTF-8/en_GB.UTF-8/en_GB.UTF-8/C/en_GB.UTF-8/en_GB.UTF-8
attached base packages:
[1] stats graphics grDevices utils datasets methods base
other attached packages:
[1] httr_0.2
loaded via a namespace (and not attached):
[1] digest_0.5.2 plyr_1.7.1 RCurl_1.95-1.1 stringr_0.6.1 tools_2.15.1
编辑：
因此，在进一步尝试遵循@hadley建议的文档时，这是我尝试并得到的。。。任何关于我哪里出错的有用提示都将不胜感激…：
require(httr)
aws.key <- "xxxxxxx"
aws.secret <- "xxxxxxxxxxxx"
verb <- "GET"
zone <- "ec2.amazonaws.com"
func <- "DescribeImages"
ami.number <- "ami-xxxxxxxxx"
params <- list(paste0("ImageId.1=",ami.number),
"Version=2012-10-01",
"Expires=2012-11-20T12%3A00%3A00Z")
# adding in method and key parameters for creation of string to sign
orig.len.params <- length(params)
params.w.method.key <- params
params.w.method.key[[orig.len.params+1]] <- "SignatureVersion=2"
params.w.method.key[[orig.len.params+2]] <- "SignatureMethod=HmacSHA1"
params.w.method.key[[orig.len.params+3]] <- paste0("AWSAccessKeyId=",aws.key)
# String to sign (s2s)
s2s <- paste(c(paste0(verb,"n",zone,"n","/n","AWSAccessKeyId=",aws.key),paste0("Action=",func),paste(sort(unlist(params.w.method.key)),collapse="&")),collapse="&")
# Signature(sig)
sig <- hmac_sha1(aws.secret, s2s)
# adding in signature, method and key parameters for signed request url generation
params.w.sig.method.key <- params
params.w.sig.method.key[[orig.len.params+1]] <- paste0("Signature=",sig)
params.w.sig.method.key[[orig.len.params+2]] <- "SignatureVersion=2"
params.w.sig.method.key[[orig.len.params+3]] <- "SignatureMethod=HmacSHA1"
params.w.sig.method.key[[orig.len.params+4]] <- paste0("AWSAccessKeyId=",aws.key)
# Signed request (sr)
sr <- paste(c(paste0("https://",zone,paste0("?Action=",func)),paste(unlist(params.w.sig.method.key),collapse="&")),collapse="&")
# GET signed request
GET(sr)
我得到了回应：
Response [https://ec2.amazonaws.com?Action=DescribeImages&ImageId.1=[ami.number.from.before]&Version=2012-10-01&Expires=2012-11-20T12%3A00%3A00Z&Signature=[sig.value.from.before]&SignatureVersion=2&SignatureMethod=HmacSHA1&AWSAccessKeyId=[aws.key.from.before]/]
Status: 401
Content-type:
<?xml version="1.0" encoding="UTF-8"?>
<Response><Errors><Error><Code>AuthFailure</Code><Message>AWS was not able to validate the provided access credentials</Message></Error></Errors><RequestID>5e10fb0b-f304-4677-9c64-98b4537c659a</RequestID></Response>
下面是我将算法逐步转换为R代码的尝试。根据我的经验，你真的想分别完成每一步，这样你就可以在每个阶段检查结果是否正确。
require("httr")
require("RCurl")
require("stringr")
# 0: get key and secret from envvars, and set up request parameters
aws.key <- Sys.getenv("AWS_KEY")
aws.secret <- Sys.getenv("AWS_SECRET_KEY")
verb <- "GET"
zone <- "ec2.amazonaws.com"
ami.number <- "ami-xxxxxxxxx"
params <- list(
Action = "DescribeImages",
ImageId.1 = ami.number,
Version = "2012-10-01",
Expires = "2012-11-20T12:00:00Z",
SignatureVersion = 2,
SignatureMethod = "HmacSHA1",
AWSAccessKeyId = aws.key)
# 1a: Sort the UTF-8 query string components by parameter name
params <- params[order(names(params))]
# 1b: URL encode the parameter name and values
params_e <- lapply(params, curlEscape)
names(params_e) <- curlEscape(names(params_e))
params_str <- str_c(names(params_e), "=", unlist(params_e), collapse = "&")
params_str <- gsub("%2E",".",gsub("%2D","-",params_str))
# 2: Create the string to sign
string_to_sign <- str_c(
toupper(verb), "n",
tolower(zone), "n",
"/", "n",
params_str
)
# 3: Calculate an RFC 2104-compliant HMAC
# 4: Convert the resulting value to base64.
hmac <- hmac_sha1(aws.secret, string_to_sign)
params$Signature <- hmac
GET(paste0("https://",zone),query=params)