ValueError Sometimes Raised When Authenticating

[jusexton]

A ValueError is sometimes being raised when attempting to authenticate credentials. The error occurs when a salt value contains a leading dash. For example: -16e462a84f2df159eee0c14642974ee7. This seems to only happen when a given username does not exist within the userpool? But not always.

The value error contains this message: non-hexadecimal number found in fromhex() arg at position 0

I have tracked it down to this snippet (line 174 in aws_srp.py):

x_value = hex_to_long(hex_hash(pad_hex(salt) + username_password_hash))

in the hex_hash function:

def hex_hash(hex_string):
    return hash_sha256(bytearray.fromhex(hex_string))

I would submit a fix but I am not sure how the application is expected to handle these kinds of scenarios.

[jusexton]

Looks like this project is having similar issues: aws/aws-sdk-net-extensions-cognito#48