fileInput fail if missing column

I was wondering if it would be possible to modify the accept argument in fileInput so that the user isn't allowed to upload a file if it's missing a certain column name and how you'd go about doing that?

Using the example as a starting point for code

ui <- fluidPage(
  sidebarLayout(
    sidebarPanel(
      fileInput("file1", "Choose CSV File",
        accept = c(
          "text/csv",
          "text/comma-separated-values,text/plain",
          ".csv")
        ),
      tags$hr(),
      checkboxInput("header", "Header", TRUE)
    ),
    mainPanel(
      tableOutput("contents")
    )
  )
)

server <- function(input, output) {
  output$contents <- renderTable({
    inFile <- input$file1

    if (is.null(inFile))
      return(NULL)

    read.csv(inFile$datapath, header = input$header)
  })
}

shinyApp(ui, server)
}

Use one of the validation approaches described in https://mastering-shiny.org/action-feedback.html#validate?

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