Storage lockers may be owned by the unit owner or controlled by the condominium corporation.
Look to your governing declaration for clarity. When purchasing a condo, the deed may specify storage unit number or physical location if part of your purchase. The corporation remains responsible for maintaining common storage areas which may include walkways and doors. Locker owners may store virtually anything they want in these spaces so long as nothing impacts on other lockers and common areas. Flammable items are likely prohibited. Open food items, which attract pests that can infiltrate spaces and constitute a health hazard, are prohibited.
When the corporation declaration states that the storage unit is part of the common area and under control of the corporation, lockers may be assigned and managed as they deem appropriate.