Validate tx/sign body and use BaseReq

[fedekunze]

Summary

POST body is not validated because it doesn't use BaseReq nor the StdTx.ValidateBasic()

Problem Definition

We are using SignBody for POST tx/sign but the StdTx is not validated at any point of the request.

cosmos-sdk/x/auth/client/rest/sign.go

Lines 15 to 24 in c9ef680

	// SignBody defines the properties of a sign request's body.
	type SignBody struct {
	Tx auth.StdTx `json:"tx"`
	LocalAccountName string `json:"name"`
	Password string `json:"password"`
	ChainID string `json:"chain_id"`
	AccountNumber uint64 `json:"account_number"`
	Sequence uint64 `json:"sequence"`
	AppendSig bool `json:"append_sig"`
	}

Proposal

Use BaseReq with its validation function and use StdTx.Validate() to validate the transaction.

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[alexanderbez]

Awesome! While we're at it, can we also update ReadRESTReq to prefix a failed JSON unmarshal with failed to decode JSON payload: ...?

I kept trying to submit a send tx but kept getting a 400 and it was not obvious to me what was wrong.