A working version of IApiOutputCache with Redis (Has some caveats around dependencies.)

RedisApiOutputCache.cs

using System;
using System.Collections.Generic;
using System.Configuration;
using System.Linq;
using CachingFramework.Redis;
using WebApi.OutputCache.Core.Cache;

namespace Some.Cool.NameSpace.Goes.Here
{
    /// <summary>
    /// An implementation of WebApi.OutputCache.Core.Cache.IApiOutputCache that uses Redis as the cache.
    /// For more information on Asp.NET Web API CacheOutput see https://github.com/filipw/AspNetWebApi-OutputCache
    /// Must use version 0.6.0, all other versions have been broken.
    // Requires CachingFramework.Redis at least version 4.7.1
    /// </summary>
    public class RedisApiOutputCache : IApiOutputCache
    {
        static RedisApiOutputCache()
        {
            Context = new Context(ConfigurationManager.ConnectionStrings["RedisCache"].ConnectionString);
        }

        private static Context Context { get; }

        public void RemoveStartsWith(string key)
        {
            Context.Cache.InvalidateKeysByTag(key);

            Remove(key);
        }

        public T Get<T>(string key) where T : class
        {
            var result = Context.Cache.GetObject<T>(key);
            return result;
        }

        public object Get(string key)
        {
            var result = Context.Cache.GetObject<object>(key);
            return result;
        }

        public void Remove(string key)
        {
            Context.Cache.Remove(key);
        }

        public bool Contains(string key)
        {
            var pattern = "*" + key + "*";
            var contains = false;

            var keys = Context.Cache.GetKeysByPattern(pattern).ToArray();
            if (keys.Length > 0)
            {
                contains = true;
            }

            return contains;
        }

        public void Add(string key, object o, DateTimeOffset expiration, string dependsOnKey = null)
        {

            var exp = expiration - DateTime.Now;
            if (dependsOnKey == null)
            {
                dependsOnKey = key;
            }
            else
            {
                dependsOnKey = APPICATION_KEY + dependsOnKey;
            }

            Context.Cache.SetObject(key, o, new string[] { dependsOnKey }, exp);
        }

        public IEnumerable<string> AllKeys { get; private set; }
    }
}