change a rust struct to a single string and back in serde for serde_json

serde.rs

// currently MyId Serialize to a string 

#[derive(Hash, PartialEq, Eq, Debug, Clone, Deserialize, Serialize)]
pub struct MyId(pub String);

// i want to change it so that i format my string so it is safe. In this case I want to 
// base64 it. I create a ::new that does this. I want my json to stay the same and validate
// the json value is real base64. 


#[derive(Hash, PartialEq, Eq, Debug, Clone, Deserialize)]
#[serde(try_from = "String")]
pub struct MyId {
    raw_id: String,
}

impl TryFrom<String> for MyId {
    type Error = String;

    fn try_from(id: String) -> Result<Self, Self::Error> {
        match base64::decode_config(&id, base64::URL_SAFE) {
            Ok(_) => Ok(MyId { raw_id: id }),
            _ => Err(format!("can not covert string from base64 {}", id)),
        }
    }
}
impl Serialize for MyId {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.serialize_str(&self.raw_id)
    }
}