How can I make Import-DscResource dynamic? I won't know ahead of time what DSC resources will be needed as all the required parameters and the type of resource is passed in by the user.

Invoke-DscResource_Test.ps1

# Example data to feed into script.
# In real life, this is an array of hashes 
# with the required parameters for 1 or more
# custom DSC resources to provision infrastructure

# The types of resources to create will only be
# known at runtime
$ResourceData = @(
    @{
        Name = 'fileShareTest'
        Type = 'cFileShare:cCreateFileShare'
        Options = @{
            Path = 'c:\temp'
            ShareName = 'DscTest'
        }
    },
    @{
        Name = 'uacTest'
        Type = 'xSystemSecurity:xUAC'
        Options = @{
            Setting = 'AlwaysNotify'
        }
    }
)
 
$DSCConfigData = @{
    AllNodes = @(
        @{    
            NodeName = "*"       
            PSDscAllowPlainTextPassword = $true
            PSDscAllowDomainUser = $true
        }
        @{
            NodeName = 'localhost'
            Config = $ResourceData
        }
    )
}
 
function CreateResource {
    param(
        $Options
    )

    switch ($options.Type) {
        'cFileShare:cCreateFileShare' {
            cCreateFileShare $options.Name {
                ShareName = $options.Options.ShareName
                Path = $options.Options.Path
            }
        }
        'xSystemSecurity:xUAC' {
            xUAC $options.Name {
                Setting = $options.options.Setting
            }
        }
    }
}

Configuration DscCompile {
    Import-DscResource -ModuleName PSDesiredStateConfiguration
   
    # I don't want to hard code the modules to import because
    # the user is passing in the resource options at runtime
    # and will be unknown.
    # I guess I could just import all DSC resources on the system
    Import-DscResource -ModuleName cFileShare
    Import-DscResource -ModuleName xSystemSecurity
   
    # Dynamically load DSC resources
    # This doesn't work as Import-DscResouce is a keyword
    # and it doesn't support variables for ModuleName and Name parameters
    foreach ($item in $AllNodes.Config) {
        $mod = $item.Type.Split(':')[0]
        $res = $item.Type.Split(':')[1]
        # This doesn't work. ModuleName must be a constant
        #Import-DscResource -ModuleName $mod -Name $res
    }
 
    # Call function to create the actual DSC resource based on the given options
    Node $AllNodes.NodeName {
        $Node.Config | ForEach {
            
            Write-Verbose $_.Type

            # I'd like to move the logic of what resource to create to outside
            # the Configuration block. Ideally, into a seperate file.
            CreateResource -Options $_

            # Would prefer not to do this as the types of resources
            # I'd be creating will only be known at runtime
            <#
            if ($_.Type -eq 'cFileShare:cCreateFileShare') {
                cCreateFileShare 'FileShareTesting' {
                    Path = $_.Options.Path
                    ShareName = $_.Options.ShareName
                }
            } elseIf ($_.Type -eq 'xSystemSecurity:xUAC') {
                xUAC 'xUACTesting' {
                    Setting = $_.Options.Setting
                }
            }
            #>
        }
    }
}
 
$mof = DscCompile -ConfigurationData $DSCConfigData -Verbose

I'm not entirely sure why you would want to do this. I've seen a presentation once by Bartek Bielawski who used AST to do partial configs in WMF4 by combining configurations before MOF compile. I guess what you are trying to accomplish is a bit like this?

Anyway. My first thought about making Import-DscResource use dynamic input is by looking at a configuration from a different perspective. If you treat it like text, it's pretty easy. Probably not what you are looking for though.

$ResourceData = @(
    @{
        Name = 'fileShareTest'
        Type = 'cFileShare:cCreateFileShare'
        Options = @{
            Path = 'c:\temp'
            ShareName = 'DscTest'
        }
    },
    @{
        Name = 'uacTest'
        Type = 'xSystemSecurity:xUAC'
        Options = @{
            Setting = 'AlwaysNotify'
        }
    }
)

function Create-Config {
    param (
        [String] $ModuleName,
        [String] $ResourceName,
        [String] $Name,
        [String] $Options
    )
    "configuration $Name {
        import-dscresource -modulename $ModuleName

        $ResourceName $Name {
            $Options
        }
    }"
}
iex (Create-Config -ModuleName $ResourceData[1].Type.Split(':')[0] -ResourceName $ResourceData[1].Type.Split(':')[1] -Name $ResourceData[1].Name -Options ($ResourceData[1].Options.GetEnumerator() | % { "$($_.Key)='$($_.Value)'" }))
iex (Create-Config -ModuleName $ResourceData[0].Type.Split(':')[0] -ResourceName $ResourceData[0].Type.Split(':')[1] -Name $ResourceData[0].Name -Options ($ResourceData[0].Options.GetEnumerator() | % { "$($_.Key)='$($_.Value)'`n" }))
fileShareTest
uacTest