Fix Auth with device and device confirmation

[hgarcianareia]

Issue #, if available:
N/A

Description of changes:
This pull request fixes an issue where the wrong property was being passed during authentication — username was used instead of deviceKey. To address this, the correct property is now passed. As a result of this fix, several property names and method signatures were updated to reflect the correct usage and improve clarity.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[ashishdhingra]

@hgarcianareia While we review your PR, could you please remove .DS_STORE files included in this PR?

[ashishdhingra]

Change to use username instead of deviceKey was introduced in 7dc118c.

Per Signing in with a device, below pseudocode demonstrates how to calculate values for DEVICE_PASSWORD_VERIFIER challenge response:

PASSWORD_CLAIM_SECRET_BLOCK = SECRET_BLOCK
TIMESTAMP = "Tue May 27 00:09:40 UTC 2025"
k = SHA256(N || g) as a non-negative integer in big-endian
u = SHA256(SRP_A || SRP_B) as a non-negative integer in big-endian
x = SHA256(salt || SHA256(DeviceGroupKey || DeviceKey || ":" || DeviceSecret)) as a non-negative integer in big-endian
S_USER = (SRP_B - k * g^x)^(a + u * x) % N
K_USER = HKDF_HMAC_SHA256(salt=u, ikm=S_USER, info="Caldera Derived Key", length=16 bytes)
PASSWORD_CLAIM_SIGNATURE = Base64(HMAC_SHA256(key=K_USER, message=(DeviceGroupKey || DeviceKey || PASSWORD_CLAIM_SECRET_BLOCK || TIMESTAMP)))

[ashishdhingra]

@hgarcianareia Your changes revert the update made in commit 7dc118c. Do you have detailed description of issue, steps to reproduce and/or some link to specification that validates your fix? We just don't want to inadvertently break something.

EDIT: I tried to test your changes locally, but it gives Amazon.CognitoIdentityProvider.Model.NotAuthorizedException: 'Incorrect username or password.'. Refer #73 (comment) to details. Do you happen to have the repo setup steps and code for troubleshooting?

Thanks,
Ashish