Servant and a weirdness in Keycloak

When writing a small tool to interface with Keycloak I found an endpoint that require the content type to be application/json while the body should be plain text. (The details are in the issue.) Since servant assumes that the content type and the content match (I know, I'd always thought that was a safe assumption to make too) it doesn't work with ReqBody '[JSON] Text. Instead I had to create a custom type that's a combination of JSON and PlainText, something that turned out to required surprisingly little code:

data KeycloakJSON deriving (Typeable)

instance Accept KeycloakJSON where
    contentType _ = "application" // "json"

instance MimeRender KeycloakJSON Text where
    mimeRender _ = fromStrict . encodeUtf8

The bug has already been fixed in Keycloak, but I'm sure there are other APIs with similar weirdness so maybe this will be useful to someone else.