The following used to work:

```
json=$(cat <<-EOF
{
    "UserPoolId": "$user_pool",
    "Username": "$email",
    "UserAttributes": [
        {
            "Name": "name",
            "Value": "$name"
        },
        {
            "Name": "custom:default_state",
            "Value": "$default_state"
        },
        {
            "Name": "custom:default_jurisdiction",
            "Value": "$default_jurisdiction"
        },
        {
            "Name": "custom:app_roles",
            "Value": "$app_roles"
        },
        {
            "Name": "custom:app_organisations",
            "Value": "$app_organisations"
        },
        {
            "Name": "email",
            "Value": "$email"
        },
        {
            "Name": "email_verified",
            "Value": "true"
        },
        {
            "Name": "custom:default_case_type",
            "Value": "$default_case_type"
        }
    ],
    "MessageAction": "SUPPRESS"
}
EOF
)
```

But no longer works in:
```
GNU bash, version 5.1.4(1)-release (x86_64-apple-darwin20.2.0)
Copyright (C) 2020 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>

This is free software; you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
```

Some other helpful info:
1. Stripping out all of the JSON fluff and leaving only the variables and the variables are all interpolated
2. Reducing the variable count to 4 variables and the interpolation works with the remaining JSON fluff.

So some combination of {} and variables seems to have happened in latest bash.

I'm not 100% sure what version of bash I was using where this previously worked.