Terraform - Optional map(objects)

I want to use the optional parameter to pass optional parameters:

variable "clients" {
  type = map(object({
    description         = string
    initiated_login_uri = optional(string)
    allowed_clients     = optional(list(string), [])
  }))
}

resource "auth0_client" "this" {
  for_each           = var.clients
  description        = each.value.description
  initiate_login_uri = each.value.initiated_login_uri
  allowed_clients    = each.value.allowed_clients
}

For which, as I understood I should be able to send

clients = {
  client_0 = {
    description         = "Description"
    initiated_login_uri = "http://example.com"
    allowed_clients     = ["XXXXXX"]
  },
  
  client_1 = {
    description = "Description"
  }
}

But got

all map elements must have the same type

Any way to fix that? Meaning each element of a map with non-mandatory attributes?

The way you declared and set the variable clients is valid Terraform code.

Consider the following code:

variable "clients" {
  type = map(object({
    description        = string
    initiate_login_uri = optional(string)
    allowed_clients    = optional(list(string), [])
  }))
  default = {
    client_0 = {
      description        = "Description"
      initiate_login_uri = "http://example.com"
      allowed_clients    = ["XXXXXX"]
    },
    client_1 = {
      description = "Description"
    }
  }
}

output "clients" {
  value       = var.clients
  description = "Value of clients"
}

Running terraform plan using Terraform v1.9.4:

Changes to Outputs:
  + clients = {
      + client_0 = {
          + allowed_clients    = [
              + "XXXXXX",
            ]
          + description        = "Description"
          + initiate_login_uri = "http://example.com"
        }
      + client_1 = {
          + allowed_clients    = []
          + description        = "Description"
          + initiate_login_uri = null
        }
    }

The problem is that you need to ensure that the default values for initiate_login_uri and allowed_clients are valid when setting the correspondent properties of auth0_client.

For example, var.clients.initiated_login_uri default value is null but the value of auth0_client.initiate_login_uri must be an HTTPS URL or an empty string, according to auth0_client documentation.

So, instead of:

variable "clients" {
  type = map(object({
    description         = string
    initiated_login_uri = optional(string)
    allowed_clients     = optional(list(string), [])
  }))
}

Try:

variable "clients" {
  type = map(object({
    description         = string
    initiated_login_uri = optional(string, "") // <-------- changed default value
    allowed_clients     = optional(list(string), [])
  }))
}

You might need to change the default value of allowed_clients as well. If an empty array ([]) is not valid, try changing the default value to null.