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kotlinlang

I see that Parameters can be received from the `request`, but I’m trying to build and write them as a `respond`

I don’t think there is anything built in, please file an issue on github.

But I think ContentNegotiation extension is quite easy to build. If client is sending `Accept: application/x-www-form-urlencoded` of course

This is the implementation I’m going to try out :slightly_smiling_face:
```
call.respond(object : OutgoingContent.ByteArrayContent() {
    override val contentType get() = ContentType.Application.FormUrlEncoded

    override fun bytes(): ByteArray =
        mapOf(
            "error" to "invalid_request",
            "error_description" to "client_id was not valid"
        )
            .map { "${it.key}=${it.value}" }
            .joinToString(separator = "&amp;")
            .toByteArray()
})
```

I think you might need to quote key &amp; value properly

There is a function:
```
fun List&lt;Pair&lt;String, String?&gt;&gt;.formUrlEncode(): String
```

Also `fun Parameters.formUrlEncode(): String`

So, you may use something like `body = parametersOf("a", "1").formUrlEncode()`

Or rather 
```
parametersOf(
            "error" to "invalid_request",
            "error_description" to "client_id was not valid"
        ).formUrlEncode()
```

See <https://github.com/ktorio/ktor/blob/master/ktor-server/ktor-server-tests/test/io/ktor/tests/server/http/UrlEncodedTest.kt#L89>

Much better!
```
override fun bytes(): ByteArray = parametersOf(
    "error" to listOf("invalid_request"),
    "error_description" to listOf("client_id was not valid")
).formUrlEncode().toByteArray()
```

Since `formUrlEncode` returns a String, and String will automatically be sent as bytes, you don’t need custom OutgoingContent

You can just a make a function something like `respondUrlEncoded` which will have similar signature to `parametersOf` and encode them

So you will just use 
```
call.respondUrlEncoded(
    "error" to listOf("invalid_request"),
    "error_description" to listOf("client_id was not valid")
)
```

I kind of like the idea of having that take in a `Parameters` so it would abstract where they were received from and it doesn’t seem to add much at the call site ```
call.respondUrlEncoded(parametersOf(
    "error" to listOf("invalid_request"),
    "error_description" to listOf("client_id was not valid")
))```