[csharp-netcore] Configure the API key in string format for HttpSigningConfiguration

[Ghufz]

Currently, the HttpSigningConfiguration object only accepts the API key in PEM/txt file format. However, if we need to retrieve the API key from a vault or another tool in string format, it is not possible to use it directly without saving it to a file.

To address this limitation, a pull request (PR) has been made to introduce a new property called KeyString. This property allows the user to provide the API key as a string. As a result, users now have the flexibility to either provide the API key file path using the existing parameter "KeyFilePath" or provide it as a string using the newly exposed property "KeyString".

Here is the example of API key as string.

var httpSignConfig = new HttpSigningConfiguration()
{
	KeyId = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx",
	KeyString = "-----BEGIN RSA PRIVATE KEY-----\r\nxxxxxxxxxxxxxx\r\n-----END RSA PRIVATE KEY-----\r\n",
       HttpSigningHeader = new System.Collections.Generic.List<string> { "(request-target)", "Host", "Date", "Digest" }
}

Here is the sample code for API key file path

var httpSignConfig = new HttpSigningConfiguration()
{
	KeyId = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx",
	KeyFilePath = "c:\users\xyz\apikey.txt",
       HttpSigningHeader = new System.Collections.Generic.List<string> { "(request-target)", "Host", "Date", "Digest" }
}

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@wing328

[wing328]

FYI @mandrean (2017/08) @frankyjuang (2019/09) @shibayan (2020/02) @Blackclaws (2021/03) @lucamazzanti (2021/05)