refactor(core): generate response hash key if not specified in create merchant account request

[ShankarSinghC]

Type of Change

• Bugfix
• New feature
• Enhancement
• Refactoring
• Dependency updates
• Documentation
• CI/CD

Description

create a hash key if it is not present, which will be used by merchant to verify if the response is coming from hyperswitch

Additional Changes

• This PR modifies the API contract
• This PR modifies the database schema
• This PR modifies application configuration/environment variables

Motivation and Context

How did you test it?

Hash key generated screenshots

Checklist

• I formatted the code cargo +nightly fmt --all
• I addressed lints thrown by cargo clippy
• I reviewed submitted code
• I added unit tests for my changes where possible
• I added a CHANGELOG entry if applicable

[SanchithHegde]

Assuming that the hash algorithm used for calculating the signature is HMAC-SHA256 (based on this snippet), using UUID v4 as the hash key is definitely a bad idea, UUIDs must not be used for any cryptographic purposes at all. Consider using a CSPRNG to securely generate a random string instead, of length 32 or 64 characters. You can use the generate_cryptographically_secure_random_string() utility function for the same.

hyperswitch/crates/common_utils/src/crypto.rs

Lines 305 to 312 in c1b631b

	/// Generate a random string using a cryptographically secure pseudo-random number generator
	/// (CSPRNG). Typically used for generating (readable) keys and passwords.
	#[inline]
	pub fn generate_cryptographically_secure_random_string(length: usize) -> String {
	use rand::distributions::DistString;
	rand::distributions::Alphanumeric.sample_string(&mut rand::rngs::OsRng, length)
	}