[feature] Allow IP range to for allowed freeradius hosts

[atb00ker]

Currently, we can only give IP address of freeradius server allowed to interact with openwisp-radius by using the OPENWISP_RADIUS_FREERADIUS_ALLOWED_HOSTS option but this is not sufficient if the IP is not fixed, example in docker-openwisp, the IP address can be in range "172.18.0.0/16".

Hence, we need to allow user to enter IP range as well.

[Sachin-NK]

can you assign it to me @atb00ker

[UltraBot05]

Hello @atb00ker, @nemesifier. I'd like to take on this issue.

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Proposed Fix:
I will implement CIDR range support for FREERADIUS_ALLOWED_HOSTS by utilizing Python's native ipaddress module, which allows this project to support Individual IPs and Ranges (something like 172.18.0.0/16) for authorized FreeRADIUS hosts.

[UltraBot05]

Update:
Hello @atb00ker and @nemesifier.

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I have submitted a Pull Request at openwisp-radius#694 that addresses this by allowing CIDR notation and subnets with host bits in FREERADIUS_ALLOWED_HOSTS. The validation now uses strict=False and includes defensive handling for whitespace and null values to prevent the previous crashes.

No Screenshots though.