Support adding request parameter that depends on other params about kohttp

[gokulchandra]

Thanks for explaining that @rybalkinsd, let me dig deeper and take a stab at it. I will keep you posted.

[rybalkinsd]

Need to figure out use cases

Possible API:

sign { params: Map<String, Any?> ->
    ...
}

[gokulchandra]

@rybalkinsd Can you provide more details this?

What I can understand is that we need a way to access the values set in the param block from within it?

param {
	"a" to ""
	"b" to "b"
	"sign" to sign(params) // params should refer to the previous set values of param
}

[rybalkinsd]

@gokulchandra
Here is a doc describing sign technique for AWS.

In general, there are at least two ways to solve the problem:

1. Add an interceptor that always adds a signature to a specific client requests.
   see okhttp3.internal.http.BridgeInterceptor

defaultHttpClient.fork {
    interceptors = ...
}

In my mind this interceptor can have just two params: signParameterName and signAlgorithm

2. Add a DSL method like sign(consumer: (Map<String, Any?>) -> Unit): Unit,
   however sign looks like a bad naming in this case, because method could be used for other purposes.

Note: for sign algorithms param order matters (like md5). So we need to move to the ordered data structure. LinkedHashMap for example

[rybalkinsd]

@SeanCai Could u pls provide an example of your sign function?

[rybalkinsd]

has a potential relation with #64 (also interceptor)