openapi-generator/modules/swagger-codegen/src/main/resources/csharp/modelEnum.mustache

    /// <summary>
    /// {{^description}}Gets or Sets {{{name}}}{{/description}}{{#description}}{{{description}}}{{/description}}
    /// </summary>{{#description}}
    /// <value>{{{description}}}</value>{{/description}}
    [JsonConverter(typeof(StringEnumConverter))]
    public enum {{#datatypeWithEnum}}{{.}}{{/datatypeWithEnum}}{{^datatypeWithEnum}}{{classname}}{{/datatypeWithEnum}}
    {
        {{#allowableValues}}{{#enumVars}}
        /// <summary>
        /// Enum {{name}} for {{{value}}}
        /// </summary>
        [EnumMember(Value = {{#isInteger}}"{{/isInteger}}{{#isDouble}}"{{/isDouble}}{{{value}}}{{#isInteger}}"{{/isInteger}}{{#isDouble}}"{{/isDouble}})]
        {{name}}{{#isInteger}} = {{{value}}}{{/isInteger}}{{^-last}},
        {{/-last}}{{/enumVars}}{{/allowableValues}}
    }