The following is a simple way to get all field definitions for a single object

gistfile1.txt

....

public with sharing class ExampleController {

  @AuraEnabled
  public static Map<String,CustomFieldDefinition> getOpportunityDescribes(){

    //-- Through deep binding, it is possible to retrieve the field limitations from apex
    //-- and leverage within lightning components.
    //-- However, it is often recommended to optimize them to a 

    SObjectType accountType = Schema.getGlobalDescribe().get('Account');
    Map<String,Schema.SObjectField> mfields = accountType.getDescribe().fields.getMap();
    
    Map<String,CustomFieldDefinition> results = new Map<String,CustomFieldDefinition>();
    
    //-- iterate through all mfields and assign to results

    return results;
  }
  
  class CustomFieldDefinition {
    //-- ensure that @AuraEnabled is added to each item to return
    @AuraEnabled
    public String fieldName;
    @AuraEnabled
    public Integer maxLength;
    
    public CustomFieldDefinition(Schema.SObjectField fieldDescription){
      SObject.DescribeFieldResult describe = fieldDescription.getDescribe();
      this.fieldName = describe.getName();
      this.maxLength = describe.getLength();
    }
  }
}