Case-insensitive string parameter or enum in an OpenAPI schema

I have an open API spec with a parameter like this: 

- name: platform
  in: query
  description: "Platform of the application"
  required: true
  schema:
    type: string
    enum:
      - "desktop"
      - "online"

when I get the "platform" parameter from URL , it can be like this :

platform=online or 
platform=ONLINE or 
platform=Online or 
platform=onLine  or ... any other format

but when I am going to use it , it is only valid if the parameter is all lower case like "platform=online", obviously to match the enum value.

how can I make schema to be the case insensitive and understand all types of passed parameters?

Enums are case-sensitive. To have a case-insensitive schema, you can use a regular expression pattern instead:

- name: platform
  in: query
  description: 'Platform of the application. Possible values: `desktop` or `online` (case-insensitive)'
  required: true
  schema:
    type: string
    pattern: '^[Dd][Ee][Ss][Kk][Tt][Oo][Pp]|[Oo][Nn][Ll][Ii][Nn][Ee]$'

Note that pattern is the pattern itself and does not support JavaScript regex literal syntax (/abc/i), which means you cannot specify flags like i (case insensitive search). As a result you need to specify both uppercase and lowercase letters in the pattern itself.

Alternatively, specify the possible values in the description rather than in pattern/enum, and verify the parameter values on the back end.

Here's the related discussion in the JSON Schema repository (OpenAPI uses JSON Schema to define the data types): Case Insensitive Enums?