### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

When attempting to sign some document using Localstack KMS inside a lambda container (also running on localstack), the localstack KMS listener returns some unknown error.

The KMS key and lambda containers have been created from the same CDK app deploy, and I can see all the resources in the localstack web console.

The test application I'm using to prove this behaviour is available here:
https://github.com/LukaHedt/localstack_kms_test

Instructions to run are in the main Readme, and the `/localstack/Readme.md` file.

`aws-sdk` returns an unknown error, and the localstack docker logs that I receive are available here:
https://pastebin.com/58Z3fXi3

Have done an amount of testing and can confidently claim the following:
- Have tested on multiple machines with the same outcome
- Doesn’t make a difference if I specify an ARN or a KeyID in the signing request
- Downgrading localstack versions either didn’t make a difference, or I couldn’t actually deploy a localstack container with version 0.12.20 or lower.

### Expected Behavior

KMS Sign should return a signature for the given payload.

### How are you starting LocalStack?

With a docker-compose file

### Steps To Reproduce

Test application demonstrating the current behaviour is available here:

https://github.com/LukaHedt/localstack_kms_test

Full instructions to run are in the `/localstack/Readme.md` file.


### Environment

```markdown
- OS: MacOS Monteray 12.3
- LocalStack: 0.14.0
```


### Anything else?

_No response_
"""Parses the environment variable $SERVICES with a comma-separated list of services
    and (optional) ports they should run on: 'service1:port1,service2,service3:port3'"""
    service_ports = os.environ.get("SERVICES", "").strip()
    if not service_ports:
        return DEFAULT_SERVICE_PORTS
    result = {}
    for service_port in re.split(r"\s*,\s*", service_ports):
        parts = re.split(r"[:=]", service_port)
        service = parts[0]
        key_upper = service.upper().replace("-", "_")
        port_env_name = "%s_PORT" % key_upper
        
        port_number = DEFAULT_SERVICE_PORTS.get(service)
        
        if os.environ.get(port_env_name):
            port_number = os.environ.get(port_env_name)
        
        if len(parts) > 1:
            port_number = int(parts[-1])
        
        try:
            port_number = int(port_number)
        except Exception:
            port_number = 0
        result[service] = port_number
    return result
def populate_configs(service_ports=None):