命令空间：Microsoft.Extensions.Primitives
程序集：Microsoft.Extensions.Primitives.dll
public readonly struct StringValues : IList<string>, ICollection<string>, IEnumerable<string>, IEnumerable, IReadOnlyList<string>, IReadOnlyCollection<string>, IEquatable<StringValues>, IEquatable<string>, IEquatable<string[]>
var httpHeaders = HttpContext.Request.Headers;
var signature = httpHeaders["signature"];
signature 就是 StringValues类型
//IList<string> 显式实现接口
((IList<string>)signature).IndexOf
