VPN Server Config certificate Base64 decoding seems not to work via CLI

### Describe the bug

When providing the command `az network vpn-server-config create --name "vpn-config" --resource-group "myGroup" --auth-types "Certificate" --protocols "IkeV2" --vpn-client-root-certs "myRootCert"`

an unexpected error is thrown.

I've generated the VPN root certificate based on this tutorial:
https://learn.microsoft.com/bs-latn-ba/azure/vpn-gateway/vpn-gateway-certificates-point-to-site-linux

I've uploaded / copy-pasted the exact certificate contents manually via Azure Portal and that worked fine. It seems that the Python code is not able to handle the Base64 decoding of the certificate.

### Related command

az network vpn-server-config create --name "vpn-config" --resource-group "myGroup" --auth-types "Certificate" --protocols "IkeV2" --vpn-client-root-certs "myRootCert"

### Errors

The command failed with an unexpected error. Here is the traceback:
'NoneType' object has no attribute 'decode'
Traceback (most recent call last):
File "/opt/az/lib/python3.10/site-packages/knack/cli.py", line 233, in invoke
cmd_result = self.invocation.execute(args)
File "/opt/az/lib/python3.10/site-packages/azure/cli/core/commands/__init__.py", line 663, in execute
raise ex
File "/opt/az/lib/python3.10/site-packages/azure/cli/core/commands/__init__.py", line 726, in _run_jobs_serially
results.append(self._run_job(expanded_arg, cmd_copy))
File "/opt/az/lib/python3.10/site-packages/azure/cli/core/commands/__init__.py", line 697, in _run_job
result = cmd_copy(params)
File "/opt/az/lib/python3.10/site-packages/azure/cli/core/commands/__init__.py", line 333, in __call__
return self.handler(*args, **kwargs)
File "/opt/az/lib/python3.10/site-packages/azure/cli/core/commands/command_operation.py", line 121, in handler
return op(**command_args)
File "/home/strobodov/.azure/cliextensions/virtual-wan/azext_vwan/custom.py", line 851, in create_vpn_server_config
vpn_client_root_certificates=_load_certificates_and_build_name_and_public_cert_data(VpnServerConfigVpnClientRootCertificate,
File "/home/strobodov/.azure/cliextensions/virtual-wan/azext_vwan/custom.py", line 1091, in _load_certificates_and_build_name_and_public_cert_data
pem_data.decode(), re.I)
AttributeError: 'NoneType' object has no attribute 'decode'

### Issue script & Debug output

cli.knack.cli: Command arguments: ['network', 'vpn-server-config', 'create', '--name', 'vpn-config', '--resource-group', 'rg_mkornegoor', '--auth-types', 'Certificate', '--protocols', 'IkeV2', '--vpn-client-root-certs', 'azureCert', '--debug']
cli.knack.cli: __init__ debug log:
Enable color in terminal.
cli.knack.cli: Event: Cli.PreExecute []
cli.knack.cli: Event: CommandParser.OnGlobalArgumentsCreate [, , ]
cli.knack.cli: Event: CommandInvoker.OnPreCommandTableCreate []
cli.azure.cli.core: Modules found from index for 'network': ['azure.cli.command_modules.network', 'azure.cli.command_modules.privatedns', 'azext_vwan']
cli.azure.cli.core: Loading command modules:
cli.azure.cli.core: Name Load Time Groups Commands
cli.azure.cli.core: network 0.510 112 341
cli.azure.cli.core: privatedns 0.004 14 66
cli.azure.cli.core: Total (2) 0.515 126 407
cli.azure.cli.core: These extensions are not installed and will be skipped: ['azext_ai_examples', 'azext_next']
cli.azure.cli.core: Loading extensions:
cli.azure.cli.core: Name Load Time Groups Commands Directory
cli.azure.cli.core: virtual-wan 0.012 20 76 /home/strobodov/.azure/cliextensions/virtual-wan
cli.azure.cli.core: Total (1) 0.012 20 76
cli.azure.cli.core: Loaded 144 groups, 483 commands.
cli.azure.cli.core: Found a match in the command table.
cli.azure.cli.core: Raw command : network vpn-server-config create
cli.azure.cli.core: Command table: network vpn-server-config create
cli.knack.cli: Event: CommandInvoker.OnPreCommandTableTruncate []
cli.azure.cli.core.azlogging: metadata file logging enabled - writing logs to '/home/strobodov/.azure/commands/2023-06-25.10-17-35.network_vpn-server-config_create.12901.log'.
az_command_data_logger: command args: network vpn-server-config create --name {} --resource-group {} --auth-types {} --protocols {} --vpn-client-root-certs {} --debug
cli.knack.cli: Event: CommandInvoker.OnPreArgumentLoad [.add_subscription_parameter at 0x7fbd1f773760>]
cli.knack.cli: Event: CommandInvoker.OnPostArgumentLoad []
cli.knack.cli: Event: CommandInvoker.OnPostCommandTableCreate [.add_ids_arguments at 0x7fbd1f7b96c0>, .add_cache_arguments at 0x7fbd1f7b97e0>]
cli.knack.cli: Event: CommandInvoker.OnCommandTableLoaded []
cli.knack.cli: Event: CommandInvoker.OnPreParseArgs []
cli.knack.cli: Event: CommandInvoker.OnPostParseArgs [, , .parse_ids_arguments at 0x7fbd1f7b9750>]
az_command_data_logger: extension name: virtual-wan
az_command_data_logger: extension version: 0.2.17
cli.azure.cli.core.commands.client_factory: Getting management service client client_type=ResourceManagementClient
cli.azure.cli.core.auth.persistence: build_persistence: location='/home/strobodov/.azure/msal_token_cache.json', encrypt=False
cli.azure.cli.core.auth.binary_cache: load: /home/strobodov/.azure/msal_http_cache.bin
urllib3.util.retry: Converted retries value: 1 -> Retry(total=1, connect=None, read=None, redirect=None, status=None)
msal.authority: openid_config = {'token_endpoint': 'https://login.microsoftonline.com/dce8a5e3-785a-419b-ad59-e6d13eb2e922/oauth2/v2.0/token', 'token_endpoint_auth_methods_supported': ['client_secret_post', 'private_key_jwt', 'client_secret_basic'], 'jwks_uri': 'https://login.microsoftonline.com/dce8a5e3-785a-419b-ad59-e6d13eb2e922/discovery/v2.0/keys', 'response_modes_supported': ['query', 'fragment', 'form_post'], 'subject_types_supported': ['pairwise'], 'id_token_signing_alg_values_supported': ['RS256'], 'response_types_supported': ['code', 'id_token', 'code id_token', 'id_token token'], 'scopes_supported': ['openid', 'profile', 'email', 'offline_access'], 'issuer': 'https://login.microsoftonline.com/dce8a5e3-785a-419b-ad59-e6d13eb2e922/v2.0', 'request_uri_parameter_supported': False, 'userinfo_endpoint': 'https://graph.microsoft.com/oidc/userinfo', 'authorization_endpoint': 'https://login.microsoftonline.com/dce8a5e3-785a-419b-ad59-e6d13eb2e922/oauth2/v2.0/authorize', 'device_authorization_endpoint': 'https://login.microsoftonline.com/dce8a5e3-785a-419b-ad59-e6d13eb2e922/oauth2/v2.0/devicecode', 'http_logout_supported': True, 'frontchannel_logout_supported': True, 'end_session_endpoint': 'https://login.microsoftonline.com/dce8a5e3-785a-419b-ad59-e6d13eb2e922/oauth2/v2.0/logout', 'claims_supported': ['sub', 'iss', 'cloud_instance_name', 'cloud_instance_host_name', 'cloud_graph_host_name', 'msgraph_host', 'aud', 'exp', 'iat', 'auth_time', 'acr', 'nonce', 'preferred_username', 'name', 'tid', 'ver', 'at_hash', 'c_hash', 'email'], 'kerberos_endpoint': 'https://login.microsoftonline.com/dce8a5e3-785a-419b-ad59-e6d13eb2e922/kerberos', 'tenant_region_scope': 'EU', 'cloud_instance_name': 'microsoftonline.com', 'cloud_graph_host_name': 'graph.windows.net', 'msgraph_host': 'graph.microsoft.com', 'rbac_url': 'https://pas.windows.net'}
msal.application: Broker enabled? False
cli.azure.cli.core.auth.credential_adaptor: CredentialAdaptor.get_token: scopes=('https://management.core.windows.net//.default',), kwargs={}
cli.azure.cli.core.auth.msal_authentication: UserCredential.get_token: scopes=('https://management.core.windows.net//.default',), claims=None, kwargs={}
msal.application: Cache hit an AT
msal.telemetry: Generate or reuse correlation_id: 4928f51d-99f3-465a-9a0a-f015d10830c6
cli.azure.cli.core.sdk.policies: Request URL: 'https://management.azure.com/subscriptions/0b32040e-ecfe-4a33-99eb-7d5e9ab4d7f3/resourcegroups/rg_mkornegoor?api-version=2022-09-01'
cli.azure.cli.core.sdk.policies: Request method: 'GET'
cli.azure.cli.core.sdk.policies: Request headers:
cli.azure.cli.core.sdk.policies: 'Accept': 'application/json'
cli.azure.cli.core.sdk.policies: 'x-ms-client-request-id': '80e88c2b-1341-11ee-a585-b9e3dbffb81c'
cli.azure.cli.core.sdk.policies: 'CommandName': 'network vpn-server-config create'
cli.azure.cli.core.sdk.policies: 'ParameterSetName': '--name --resource-group --auth-types --protocols --vpn-client-root-certs --debug'
cli.azure.cli.core.sdk.policies: 'User-Agent': 'AZURECLI/2.49.0 (DEB) azsdk-python-azure-mgmt-resource/22.0.0 Python/3.10.10 (Linux-6.1.0-0.deb11.7-cloud-amd64-x86_64-with-glibc2.31)'
cli.azure.cli.core.sdk.policies: 'Authorization': '*****'
cli.azure.cli.core.sdk.policies: Request body:
cli.azure.cli.core.sdk.policies: This request has no body
urllib3.connectionpool: Starting new HTTPS connection (1): management.azure.com:443
urllib3.connectionpool: https://management.azure.com:443 "GET /subscriptions/0b32040e-ecfe-4a33-99eb-7d5e9ab4d7f3/resourcegroups/rg_mkornegoor?api-version=2022-09-01 HTTP/1.1" 200 285
cli.azure.cli.core.sdk.policies: Response status: 200
cli.azure.cli.core.sdk.policies: Response headers:
cli.azure.cli.core.sdk.policies: 'Cache-Control': 'no-cache'
cli.azure.cli.core.sdk.policies: 'Pragma': 'no-cache'
cli.azure.cli.core.sdk.policies: 'Content-Type': 'application/json; charset=utf-8'
cli.azure.cli.core.sdk.policies: 'Content-Encoding': 'gzip'
cli.azure.cli.core.sdk.policies: 'Expires': '-1'
cli.azure.cli.core.sdk.policies: 'Vary': 'Accept-Encoding'
cli.azure.cli.core.sdk.policies: 'x-ms-ratelimit-remaining-subscription-reads': '11999'
cli.azure.cli.core.sdk.policies: 'x-ms-request-id': 'f45a4876-1121-4b7b-8cf9-dfe5d3cec88b'
cli.azure.cli.core.sdk.policies: 'x-ms-correlation-request-id': 'f45a4876-1121-4b7b-8cf9-dfe5d3cec88b'
cli.azure.cli.core.sdk.policies: 'x-ms-routing-request-id': 'WESTEUROPE:20230625T101736Z:f45a4876-1121-4b7b-8cf9-dfe5d3cec88b'
cli.azure.cli.core.sdk.policies: 'Strict-Transport-Security': 'max-age=31536000; includeSubDomains'
cli.azure.cli.core.sdk.policies: 'X-Content-Type-Options': 'nosniff'
cli.azure.cli.core.sdk.policies: 'Date': 'Sun, 25 Jun 2023 10:17:35 GMT'
cli.azure.cli.core.sdk.policies: 'Content-Length': '285'
cli.azure.cli.core.sdk.policies: Response content:
cli.azure.cli.core.sdk.policies: {"id":"/subscriptions/0b32040e-ecfe-4a33-99eb-7d5e9ab4d7f3/resourceGroups/rg_mkornegoor","name":"rg_mkornegoor","type":"Microsoft.Resources/resourceGroups","location":"westeurope","properties":{"provisioningState":"Succeeded"}}
cli.azure.cli.core.commands.validators: using location 'westeurope' from resource group 'rg_mkornegoor'
cli.azure.cli.core.commands.client_factory: Getting management service client client_type=NetworkManagementClient
urllib3.util.retry: Converted retries value: 1 -> Retry(total=1, connect=None, read=None, redirect=None, status=None)
msal.authority: openid_config = {'token_endpoint': 'https://login.microsoftonline.com/dce8a5e3-785a-419b-ad59-e6d13eb2e922/oauth2/v2.0/token', 'token_endpoint_auth_methods_supported': ['client_secret_post', 'private_key_jwt', 'client_secret_basic'], 'jwks_uri': 'https://login.microsoftonline.com/dce8a5e3-785a-419b-ad59-e6d13eb2e922/discovery/v2.0/keys', 'response_modes_supported': ['query', 'fragment', 'form_post'], 'subject_types_supported': ['pairwise'], 'id_token_signing_alg_values_supported': ['RS256'], 'response_types_supported': ['code', 'id_token', 'code id_token', 'id_token token'], 'scopes_supported': ['openid', 'profile', 'email', 'offline_access'], 'issuer': 'https://login.microsoftonline.com/dce8a5e3-785a-419b-ad59-e6d13eb2e922/v2.0', 'request_uri_parameter_supported': False, 'userinfo_endpoint': 'https://graph.microsoft.com/oidc/userinfo', 'authorization_endpoint': 'https://login.microsoftonline.com/dce8a5e3-785a-419b-ad59-e6d13eb2e922/oauth2/v2.0/authorize', 'device_authorization_endpoint': 'https://login.microsoftonline.com/dce8a5e3-785a-419b-ad59-e6d13eb2e922/oauth2/v2.0/devicecode', 'http_logout_supported': True, 'frontchannel_logout_supported': True, 'end_session_endpoint': 'https://login.microsoftonline.com/dce8a5e3-785a-419b-ad59-e6d13eb2e922/oauth2/v2.0/logout', 'claims_supported': ['sub', 'iss', 'cloud_instance_name', 'cloud_instance_host_name', 'cloud_graph_host_name', 'msgraph_host', 'aud', 'exp', 'iat', 'auth_time', 'acr', 'nonce', 'preferred_username', 'name', 'tid', 'ver', 'at_hash', 'c_hash', 'email'], 'kerberos_endpoint': 'https://login.microsoftonline.com/dce8a5e3-785a-419b-ad59-e6d13eb2e922/kerberos', 'tenant_region_scope': 'EU', 'cloud_instance_name': 'microsoftonline.com', 'cloud_graph_host_name': 'graph.windows.net', 'msgraph_host': 'graph.microsoft.com', 'rbac_url': 'https://pas.windows.net'}
msal.application: Broker enabled? False
cli.azure.cli.core.azclierror: Traceback (most recent call last):
File "/opt/az/lib/python3.10/site-packages/knack/cli.py", line 233, in invoke
cmd_result = self.invocation.execute(args)
File "/opt/az/lib/python3.10/site-packages/azure/cli/core/commands/__init__.py", line 663, in execute
raise ex
File "/opt/az/lib/python3.10/site-packages/azure/cli/core/commands/__init__.py", line 726, in _run_jobs_serially
results.append(self._run_job(expanded_arg, cmd_copy))
File "/opt/az/lib/python3.10/site-packages/azure/cli/core/commands/__init__.py", line 697, in _run_job
result = cmd_copy(params)
File "/opt/az/lib/python3.10/site-packages/azure/cli/core/commands/__init__.py", line 333, in __call__
return self.handler(*args, **kwargs)
File "/opt/az/lib/python3.10/site-packages/azure/cli/core/commands/command_operation.py", line 121, in handler
return op(**command_args)
File "/home/strobodov/.azure/cliextensions/virtual-wan/azext_vwan/custom.py", line 851, in create_vpn_server_config
vpn_client_root_certificates=_load_certificates_and_build_name_and_public_cert_data(VpnServerConfigVpnClientRootCertificate,
File "/home/strobodov/.azure/cliextensions/virtual-wan/azext_vwan/custom.py", line 1091, in _load_certificates_and_build_name_and_public_cert_data
pem_data.decode(), re.I)
AttributeError: 'NoneType' object has no attribute 'decode'

cli.azure.cli.core.azclierror: The command failed with an unexpected error. Here is the traceback:
az_command_data_logger: The command failed with an unexpected error. Here is the traceback:
cli.azure.cli.core.azclierror: 'NoneType' object has no attribute 'decode'
Traceback (most recent call last):
File "/opt/az/lib/python3.10/site-packages/knack/cli.py", line 233, in invoke
cmd_result = self.invocation.execute(args)
File "/opt/az/lib/python3.10/site-packages/azure/cli/core/commands/__init__.py", line 663, in execute
raise ex
File "/opt/az/lib/python3.10/site-packages/azure/cli/core/commands/__init__.py", line 726, in _run_jobs_serially
results.append(self._run_job(expanded_arg, cmd_copy))
File "/opt/az/lib/python3.10/site-packages/azure/cli/core/commands/__init__.py", line 697, in _run_job
result = cmd_copy(params)
File "/opt/az/lib/python3.10/site-packages/azure/cli/core/commands/__init__.py", line 333, in __call__
return self.handler(*args, **kwargs)
File "/opt/az/lib/python3.10/site-packages/azure/cli/core/commands/command_operation.py", line 121, in handler
return op(**command_args)
File "/home/strobodov/.azure/cliextensions/virtual-wan/azext_vwan/custom.py", line 851, in create_vpn_server_config
vpn_client_root_certificates=_load_certificates_and_build_name_and_public_cert_data(VpnServerConfigVpnClientRootCertificate,
File "/home/strobodov/.azure/cliextensions/virtual-wan/azext_vwan/custom.py", line 1091, in _load_certificates_and_build_name_and_public_cert_data
pem_data.decode(), re.I)
AttributeError: 'NoneType' object has no attribute 'decode'
az_command_data_logger: 'NoneType' object has no attribute 'decode'
Traceback (most recent call last):
File "/opt/az/lib/python3.10/site-packages/knack/cli.py", line 233, in invoke
cmd_result = self.invocation.execute(args)
File "/opt/az/lib/python3.10/site-packages/azure/cli/core/commands/__init__.py", line 663, in execute
raise ex
File "/opt/az/lib/python3.10/site-packages/azure/cli/core/commands/__init__.py", line 726, in _run_jobs_serially
results.append(self._run_job(expanded_arg, cmd_copy))
File "/opt/az/lib/python3.10/site-packages/azure/cli/core/commands/__init__.py", line 697, in _run_job
result = cmd_copy(params)
File "/opt/az/lib/python3.10/site-packages/azure/cli/core/commands/__init__.py", line 333, in __call__
return self.handler(*args, **kwargs)
File "/opt/az/lib/python3.10/site-packages/azure/cli/core/commands/command_operation.py", line 121, in handler
return op(**command_args)
File "/home/strobodov/.azure/cliextensions/virtual-wan/azext_vwan/custom.py", line 851, in create_vpn_server_config
vpn_client_root_certificates=_load_certificates_and_build_name_and_public_cert_data(VpnServerConfigVpnClientRootCertificate,
File "/home/strobodov/.azure/cliextensions/virtual-wan/azext_vwan/custom.py", line 1091, in _load_certificates_and_build_name_and_public_cert_data
pem_data.decode(), re.I)
AttributeError: 'NoneType' object has no attribute 'decode'

### Expected behavior

I would expect the command to except the base64 encoded input. The `--vpn-client-root-certs` flag expects a filepath and the file contains the base64 encoded certificate.

### Environment Summary

azure-cli 2.49.0

core 2.49.0
telemetry 1.0.8

Extensions:
virtual-wan 0.2.17

Dependencies:
msal 1.20.0
azure-mgmt-resource 22.0.0

Python location '/opt/az/bin/python3'
Extensions directory '/home/strobodov/.azure/cliextensions'

Python (Linux) 3.10.10 (main, May 19 2023, 08:20:28) [GCC 10.2.1 20210110]

Legal docs and information: aka.ms/AzureCliLegal

Your CLI is up-to-date.

Static hostname: hoppert
Icon name: computer-vm
Chassis: vm
Machine ID: b81860115f824419b2e69f41961498ca
Boot ID: a606f12c8d544dddaf08abb0374b6e21
Virtualization: microsoft
Operating System: Debian GNU/Linux 11 (bullseye)
Kernel: Linux 6.1.0-0.deb11.7-cloud-amd64
Architecture: x86-64

### Additional context

_No response_