diff --git a/NAMESPACE b/NAMESPACE
index feedca9..2b9d1a1 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -2,6 +2,11 @@
 
 S3method(.add_body,json)
 S3method(.add_body,multipart)
+S3method(.as_nectar_auth,"NULL")
+S3method(.as_nectar_auth,"function")
+S3method(.as_nectar_auth,default)
+S3method(.as_nectar_auth,list)
+S3method(.as_nectar_auth,nectar_auth)
 S3method(.as_nectar_request,default)
 S3method(.as_nectar_request,httr2_request)
 S3method(.as_nectar_request,nectar_request)
@@ -12,6 +17,8 @@ S3method(resp_tidy,default)
 S3method(resp_tidy,httr2_response)
 S3method(resp_tidy,list)
 S3method(resp_tidy,nectar_responses)
+export(auth_api_key)
+export(auth_prepare)
 export(choose_pagination_fn)
 export(compact_nested_list)
 export(do_if_fn_defined)
diff --git a/R/aaa-shared_params.R b/R/aaa-shared_params.R
index b82cd1e..6cb7e53 100644
--- a/R/aaa-shared_params.R
+++ b/R/aaa-shared_params.R
@@ -6,14 +6,15 @@
 #'   where a request is coming from. We automatically include information about
 #'   your package and nectar, but use this to provide additional details.
 #'   Default `NULL`.
-#' @param api_key (`length-1 character`) The API key to use.
+#' @param api_key (`length-1 character` or `NULL`) The API key to use. If this
+#'   value is `NULL`, the key will be removed from the request. If this value is
+#'   `NA` or an empty string, the request is returned unchanged when the
+#'   prepared auth is applied.
 #' @param arg (`length-1 character`) An argument name as a string. This argument
 #'   will be mentioned in error messages as the input that is at the origin of a
 #'   problem.
-#' @param auth_args (`list`) An optional list of arguments to the `auth_fn`
-#'   function.
-#' @param auth_fn (`function`) A function to use to authenticate the request. By
-#'   default (`NULL`), no authentication is performed.
+#' @param auth (`nectar_auth` or `NULL`) Authentication prepared with
+#'   [auth_prepare()]. By default (`NULL`), no authentication is performed.
 #' @param base_url (`length-1 character`) The part of the url that is shared by
 #'   all calls to the API. In some cases there may be a family of base URLs,
 #'   from which you will need to choose one.
@@ -35,6 +36,8 @@
 #'   other than `GET` or `POST`, supply it. Case is ignored.
 #' @param mime_type (`length-1 character`) The mime type of any files present in
 #'   the body. Some APIs allow you to leave this as NULL for them to guess.
+#' @param location (`length-1 character`) Where the API key should be passed.
+#'   One of `"header"` (default), `"query"`, or `"cookie"`.
 #' @param name (`length-1 character`) The name of a package or other thing to
 #'   add to or remove from the user agent string.
 #' @param pagination_fn (`function`) A function that takes the previous response
@@ -44,7 +47,8 @@
 #'   [httr2::iterate_with_offset()]. This function will be extracted from the
 #'   request by [req_perform_opinionated()] and passed on as `next_req` to
 #'   [httr2::req_perform_iterative()].
-#' @param parameter_name (`length-1 character`) The name to use for the API key.
+#' @param parameter_name (`length-1 character`) The name of the parameter to use
+#'   in the header, query, or cookie.
 #' @param path (`character` or `list`) The route to an API endpoint. Optionally,
 #'   a list or character vector with the path as one or more unnamed arguments
 #'   (which will be concatenated with "/") plus named arguments to
diff --git a/R/auth_prepare.R b/R/auth_prepare.R
new file mode 100644
index 0000000..9aab3bb
--- /dev/null
+++ b/R/auth_prepare.R
@@ -0,0 +1,76 @@
+#' Prepare authentication independent of a request
+#'
+#' This constructor stores an authentication function and arguments so the same
+#' authentication strategy can be reused across requests.
+#'
+#' @inheritParams .shared-params
+#' @param auth_fn (`function`) A function to use to authenticate a request.
+#' @param ... (`any`) Arguments to pass to `auth_fn`.
+#' @returns A list with class `"nectar_auth"` and elements `auth_fn` and
+#'   `auth_args`.
+#' @family opinionated auth functions
+#' @export
+#'
+#' @examples
+#' auth_prepare(req_auth_api_key, "X-API-Key", api_key = "my-api-key")
+auth_prepare <- function(auth_fn, ..., call = rlang::caller_env()) {
+  auth_fn <- rlang::as_function(auth_fn, call = call)
+  .as_nectar_auth(
+    list(auth_fn = auth_fn, auth_args = rlang::list2(...)),
+    call = call
+  )
+}
+
+.as_nectar_auth <- function(auth, call = rlang::caller_env()) {
+  UseMethod(".as_nectar_auth")
+}
+
+#' @export
+.as_nectar_auth.nectar_auth <- function(auth, call = rlang::caller_env()) {
+  return(auth)
+}
+
+#' @export
+.as_nectar_auth.NULL <- function(auth, call = rlang::caller_env()) {
+  return(list(auth_fn = NULL, auth_args = list()))
+}
+
+#' @export
+.as_nectar_auth.function <- function(auth, call = rlang::caller_env()) {
+  .as_nectar_auth(list(auth_fn = auth), call = call)
+}
+
+#' @export
+.as_nectar_auth.list <- function(auth, call = rlang::caller_env()) {
+  if (!("auth_fn" %in% names(auth))) {
+    return(NextMethod())
+  }
+  auth_args <- stbl::to_lst(auth$auth_args) %||% list()
+  if (setequal(names(auth), c("auth_fn", "auth_args"))) {
+    auth$auth_args <- auth_args
+    class(auth) <- "nectar_auth"
+    return(auth)
+  }
+  structure(
+    list(
+      auth_fn = auth$auth_fn,
+      auth_args = c(
+        auth_args,
+        auth[setdiff(names(auth), c("auth_fn", "auth_args"))]
+      )
+    ),
+    class = "nectar_auth"
+  )
+}
+
+#' @export
+.as_nectar_auth.default <- function(auth, call = rlang::caller_env()) {
+  .nectar_abort(
+    c(
+      "{.arg {auth}} must be `NULL` or a {.cls nectar_auth}.",
+      x = "{.arg {auth}} is {.obj_type_friendly {auth}}."
+    ),
+    subclass = "unsupported_auth_class",
+    call = call
+  )
+}
diff --git a/R/req_auth_api_key.R b/R/req_auth_api_key.R
index 839a88d..2239de5 100644
--- a/R/req_auth_api_key.R
+++ b/R/req_auth_api_key.R
@@ -6,15 +6,10 @@
 #'
 #' @inheritParams .shared-params
 #' @inheritParams rlang::args_dots_empty
-#' @param parameter_name (`length-1 character`) The name of the parameter to use
-#'   in the header, query, or cookie.
-#' @param api_key (`length-1 character` or `NULL`) The API key to use. If this
-#'   value is `NULL`, the key will be removed from the request. If this value is
-#'   `NA` or an empty string, `req` is returned unchanged.
-#' @param location (`length-1 character`) Where the API key should be passed.
-#'   One of `"header"` (default), `"query"`, or `"cookie"`.
 #'
 #' @inherit .shared-request return
+#' @family opinionated auth functions
+#' @family opinionated request functions
 #' @export
 #'
 #' @examples
@@ -60,3 +55,35 @@ req_auth_api_key <- function(
   req <- rlang::exec(req_api_key_set, req, !!parameter_name := api_key)
   return(req)
 }
+
+#' Prepare API key authentication independent of a request
+#'
+#' This helper creates a reusable authentication object that can be passed to
+#' [req_prepare()] via `auth`.
+#'
+#' @inheritParams .shared-params
+#' @inheritParams rlang::args_dots_empty
+#' @returns A list with class `"nectar_auth"` and elements `auth_fn` and
+#'   `auth_args`.
+#' @family opinionated auth functions
+#' @export
+#'
+#' @examples
+#' auth_api_key("X-API-Key", api_key = "my-api-key")
+auth_api_key <- function(
+  parameter_name,
+  ...,
+  api_key = NULL,
+  location = c("header", "query", "cookie"),
+  call = rlang::caller_env()
+) {
+  rlang::check_dots_empty(call = call)
+  location <- rlang::arg_match(location, error_call = call)
+  auth_prepare(
+    req_auth_api_key,
+    parameter_name = parameter_name,
+    api_key = api_key,
+    location = location,
+    call = call
+  )
+}
diff --git a/R/req_prepare.R b/R/req_prepare.R
index 0144768..f716050 100644
--- a/R/req_prepare.R
+++ b/R/req_prepare.R
@@ -26,8 +26,7 @@ req_prepare <- function(
   mime_type = NULL,
   method = NULL,
   additional_user_agent = NULL,
-  auth_fn = NULL,
-  auth_args = list(),
+  auth = NULL,
   tidy_fn = NULL,
   tidy_args = list(),
   pagination_fn = NULL,
@@ -48,7 +47,8 @@ req_prepare <- function(
     method = method,
     call = call
   )
-  req <- do_if_fn_defined(req, auth_fn, !!!auth_args, call = call)
+  auth <- .as_nectar_auth(auth, call = call)
+  req <- do_if_fn_defined(req, auth$auth_fn, !!!auth$auth_args, call = call)
   if (length(pagination_fn)) {
     req <- req_pagination_policy(req, pagination_fn, call = call)
   }
diff --git a/man/auth_api_key.Rd b/man/auth_api_key.Rd
new file mode 100644
index 0000000..d98937a
--- /dev/null
+++ b/man/auth_api_key.Rd
@@ -0,0 +1,51 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/req_auth_api_key.R
+\name{auth_api_key}
+\alias{auth_api_key}
+\title{Prepare API key authentication independent of a request}
+\usage{
+auth_api_key(
+  parameter_name,
+  ...,
+  api_key = NULL,
+  location = c("header", "query", "cookie"),
+  call = rlang::caller_env()
+)
+}
+\arguments{
+\item{parameter_name}{(\verb{length-1 character}) The name of the parameter to use
+in the header, query, or cookie.}
+
+\item{...}{These dots are for future extensions and must be empty.}
+
+\item{api_key}{(\verb{length-1 character} or \code{NULL}) The API key to use. If this
+value is \code{NULL}, the key will be removed from the request. If this value is
+\code{NA} or an empty string, the request is returned unchanged when the
+prepared auth is applied.}
+
+\item{location}{(\verb{length-1 character}) Where the API key should be passed.
+One of \code{"header"} (default), \code{"query"}, or \code{"cookie"}.}
+
+\item{call}{(\code{environment}) The environment from which a function was called,
+e.g. \code{\link[rlang:caller_env]{rlang::caller_env()}} (the default). The environment will be mentioned
+in error messages as the source of the error. This argument is particularly
+useful for functions that are intended to be called as utilities inside
+other functions.}
+}
+\value{
+A list with class \code{"nectar_auth"} and elements \code{auth_fn} and
+\code{auth_args}.
+}
+\description{
+This helper creates a reusable authentication object that can be passed to
+\code{\link[=req_prepare]{req_prepare()}} via \code{auth}.
+}
+\examples{
+auth_api_key("X-API-Key", api_key = "my-api-key")
+}
+\seealso{
+Other opinionated auth functions:
+\code{\link[=auth_prepare]{auth_prepare()}},
+\code{\link[=req_auth_api_key]{req_auth_api_key()}}
+}
+\concept{opinionated auth functions}
diff --git a/man/auth_prepare.Rd b/man/auth_prepare.Rd
new file mode 100644
index 0000000..353233f
--- /dev/null
+++ b/man/auth_prepare.Rd
@@ -0,0 +1,36 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/auth_prepare.R
+\name{auth_prepare}
+\alias{auth_prepare}
+\title{Prepare authentication independent of a request}
+\usage{
+auth_prepare(auth_fn, ..., call = rlang::caller_env())
+}
+\arguments{
+\item{auth_fn}{(\code{function}) A function to use to authenticate a request.}
+
+\item{...}{(\code{any}) Arguments to pass to \code{auth_fn}.}
+
+\item{call}{(\code{environment}) The environment from which a function was called,
+e.g. \code{\link[rlang:caller_env]{rlang::caller_env()}} (the default). The environment will be mentioned
+in error messages as the source of the error. This argument is particularly
+useful for functions that are intended to be called as utilities inside
+other functions.}
+}
+\value{
+A list with class \code{"nectar_auth"} and elements \code{auth_fn} and
+\code{auth_args}.
+}
+\description{
+This constructor stores an authentication function and arguments so the same
+authentication strategy can be reused across requests.
+}
+\examples{
+auth_prepare(req_auth_api_key, "X-API-Key", api_key = "my-api-key")
+}
+\seealso{
+Other opinionated auth functions:
+\code{\link[=auth_api_key]{auth_api_key()}},
+\code{\link[=req_auth_api_key]{req_auth_api_key()}}
+}
+\concept{opinionated auth functions}
diff --git a/man/dot-shared-params.Rd b/man/dot-shared-params.Rd
index ecb9631..bd2458c 100644
--- a/man/dot-shared-params.Rd
+++ b/man/dot-shared-params.Rd
@@ -9,17 +9,17 @@ where a request is coming from. We automatically include information about
 your package and nectar, but use this to provide additional details.
 Default \code{NULL}.}
 
-\item{api_key}{(\verb{length-1 character}) The API key to use.}
+\item{api_key}{(\verb{length-1 character} or \code{NULL}) The API key to use. If this
+value is \code{NULL}, the key will be removed from the request. If this value is
+\code{NA} or an empty string, the request is returned unchanged when the
+prepared auth is applied.}
 
 \item{arg}{(\verb{length-1 character}) An argument name as a string. This argument
 will be mentioned in error messages as the input that is at the origin of a
 problem.}
 
-\item{auth_args}{(\code{list}) An optional list of arguments to the \code{auth_fn}
-function.}
-
-\item{auth_fn}{(\code{function}) A function to use to authenticate the request. By
-default (\code{NULL}), no authentication is performed.}
+\item{auth}{(\code{nectar_auth} or \code{NULL}) Authentication prepared with
+\code{\link[=auth_prepare]{auth_prepare()}}. By default (\code{NULL}), no authentication is performed.}
 
 \item{base_url}{(\verb{length-1 character}) The part of the url that is shared by
 all calls to the API. In some cases there may be a family of base URLs,
@@ -49,6 +49,9 @@ other than \code{GET} or \code{POST}, supply it. Case is ignored.}
 \item{mime_type}{(\verb{length-1 character}) The mime type of any files present in
 the body. Some APIs allow you to leave this as NULL for them to guess.}
 
+\item{location}{(\verb{length-1 character}) Where the API key should be passed.
+One of \code{"header"} (default), \code{"query"}, or \code{"cookie"}.}
+
 \item{name}{(\verb{length-1 character}) The name of a package or other thing to
 add to or remove from the user agent string.}
 
@@ -60,7 +63,8 @@ using one of the iteration helpers described in
 request by \code{\link[=req_perform_opinionated]{req_perform_opinionated()}} and passed on as \code{next_req} to
 \code{\link[httr2:req_perform_iterative]{httr2::req_perform_iterative()}}.}
 
-\item{parameter_name}{(\verb{length-1 character}) The name to use for the API key.}
+\item{parameter_name}{(\verb{length-1 character}) The name of the parameter to use
+in the header, query, or cookie.}
 
 \item{path}{(\code{character} or \code{list}) The route to an API endpoint. Optionally,
 a list or character vector with the path as one or more unnamed arguments
diff --git a/man/req_auth_api_key.Rd b/man/req_auth_api_key.Rd
index 98371af..234152a 100644
--- a/man/req_auth_api_key.Rd
+++ b/man/req_auth_api_key.Rd
@@ -23,7 +23,8 @@ in the header, query, or cookie.}
 
 \item{api_key}{(\verb{length-1 character} or \code{NULL}) The API key to use. If this
 value is \code{NULL}, the key will be removed from the request. If this value is
-\code{NA} or an empty string, \code{req} is returned unchanged.}
+\code{NA} or an empty string, the request is returned unchanged when the
+prepared auth is applied.}
 
 \item{location}{(\verb{length-1 character}) Where the API key should be passed.
 One of \code{"header"} (default), \code{"query"}, or \code{"cookie"}.}
@@ -54,3 +55,17 @@ req_auth_api_key(req, "api_key", api_key = "my-api-key", location = "query")
 # If `api_key` is NULL, the key is removed from the request
 req_auth_api_key(req, "X-API-Key", api_key = NULL)
 }
+\seealso{
+Other opinionated auth functions:
+\code{\link[=auth_api_key]{auth_api_key()}},
+\code{\link[=auth_prepare]{auth_prepare()}}
+
+Other opinionated request functions:
+\code{\link[=req_init]{req_init()}},
+\code{\link[=req_modify]{req_modify()}},
+\code{\link[=req_pagination_policy]{req_pagination_policy()}},
+\code{\link[=req_prepare]{req_prepare()}},
+\code{\link[=req_tidy_policy]{req_tidy_policy()}}
+}
+\concept{opinionated auth functions}
+\concept{opinionated request functions}
diff --git a/man/req_init.Rd b/man/req_init.Rd
index f30dfbc..4ff141b 100644
--- a/man/req_init.Rd
+++ b/man/req_init.Rd
@@ -46,6 +46,7 @@ req_init(
 }
 \seealso{
 Other opinionated request functions:
+\code{\link[=req_auth_api_key]{req_auth_api_key()}},
 \code{\link[=req_modify]{req_modify()}},
 \code{\link[=req_pagination_policy]{req_pagination_policy()}},
 \code{\link[=req_prepare]{req_prepare()}},
diff --git a/man/req_modify.Rd b/man/req_modify.Rd
index 3b4dfd8..5d0ebde 100644
--- a/man/req_modify.Rd
+++ b/man/req_modify.Rd
@@ -60,6 +60,7 @@ req_modify(req_base, query = c("param1" = "value1", "param2" = "value2"))
 }
 \seealso{
 Other opinionated request functions:
+\code{\link[=req_auth_api_key]{req_auth_api_key()}},
 \code{\link[=req_init]{req_init()}},
 \code{\link[=req_pagination_policy]{req_pagination_policy()}},
 \code{\link[=req_prepare]{req_prepare()}},
diff --git a/man/req_pagination_policy.Rd b/man/req_pagination_policy.Rd
index 41bfdb6..346810f 100644
--- a/man/req_pagination_policy.Rd
+++ b/man/req_pagination_policy.Rd
@@ -40,6 +40,7 @@ req_pagination_policy(req, httr2::iterate_with_offset("page"))
 }
 \seealso{
 Other opinionated request functions:
+\code{\link[=req_auth_api_key]{req_auth_api_key()}},
 \code{\link[=req_init]{req_init()}},
 \code{\link[=req_modify]{req_modify()}},
 \code{\link[=req_prepare]{req_prepare()}},
diff --git a/man/req_prepare.Rd b/man/req_prepare.Rd
index cd1a159..05b4eaf 100644
--- a/man/req_prepare.Rd
+++ b/man/req_prepare.Rd
@@ -13,8 +13,7 @@ req_prepare(
   mime_type = NULL,
   method = NULL,
   additional_user_agent = NULL,
-  auth_fn = NULL,
-  auth_args = list(),
+  auth = NULL,
   tidy_fn = NULL,
   tidy_args = list(),
   pagination_fn = NULL,
@@ -53,11 +52,8 @@ where a request is coming from. We automatically include information about
 your package and nectar, but use this to provide additional details.
 Default \code{NULL}.}
 
-\item{auth_fn}{(\code{function}) A function to use to authenticate the request. By
-default (\code{NULL}), no authentication is performed.}
-
-\item{auth_args}{(\code{list}) An optional list of arguments to the \code{auth_fn}
-function.}
+\item{auth}{(\code{nectar_auth} or \code{NULL}) Authentication prepared with
+\code{\link[=auth_prepare]{auth_prepare()}}. By default (\code{NULL}), no authentication is performed.}
 
 \item{tidy_fn}{(\code{function}) A function that will be invoked by \code{\link[=resp_tidy]{resp_tidy()}}
 to tidy the response.}
@@ -97,6 +93,7 @@ req_prepare(
 }
 \seealso{
 Other opinionated request functions:
+\code{\link[=req_auth_api_key]{req_auth_api_key()}},
 \code{\link[=req_init]{req_init()}},
 \code{\link[=req_modify]{req_modify()}},
 \code{\link[=req_pagination_policy]{req_pagination_policy()}},
diff --git a/man/req_tidy_policy.Rd b/man/req_tidy_policy.Rd
index 5bf17af..a3d9bbf 100644
--- a/man/req_tidy_policy.Rd
+++ b/man/req_tidy_policy.Rd
@@ -40,6 +40,7 @@ req_tidy_policy(req, httr2::resp_body_json, list(simplifyVector = TRUE))
 }
 \seealso{
 Other opinionated request functions:
+\code{\link[=req_auth_api_key]{req_auth_api_key()}},
 \code{\link[=req_init]{req_init()}},
 \code{\link[=req_modify]{req_modify()}},
 \code{\link[=req_pagination_policy]{req_pagination_policy()}},
diff --git a/tests/testthat/test-auth_prepare.R b/tests/testthat/test-auth_prepare.R
new file mode 100644
index 0000000..4af138a
--- /dev/null
+++ b/tests/testthat/test-auth_prepare.R
@@ -0,0 +1,61 @@
+test_that("auth_prepare() constructs nectar_auth objects (#81)", {
+  test_result <- auth_prepare(req_auth_api_key, "parm", api_key = "my_key")
+  expect_s3_class(test_result, "nectar_auth")
+  expect_identical(test_result$auth_fn, req_auth_api_key)
+  expect_identical(
+    test_result$auth_args,
+    list("parm", api_key = "my_key")
+  )
+})
+
+test_that(".as_nectar_auth() returns nectar_auth objects unchanged (#81)", {
+  test_input <- auth_prepare(
+    auth_fn = req_auth_api_key,
+    auth_args = list(parameter_name = "parm")
+  )
+  test_result <- .as_nectar_auth(test_input)
+  expect_identical(test_result, test_input)
+})
+
+test_that(".as_nectar_auth() returns NULL auth_fn and empty auth_args for NULL input (#81)", {
+  test_result <- .as_nectar_auth(NULL)
+  expect_identical(test_result$auth_fn, NULL)
+  expect_identical(test_result$auth_args, list())
+})
+
+test_that(".as_nectar_auth() errors for list without auth_fn (#81)", {
+  stbl::expect_pkg_error_classes(
+    .as_nectar_auth(list(auth_args = list(parameter_name = "parm"))),
+    "nectar",
+    class = "unsupported_auth_class"
+  )
+})
+
+test_that(".as_nectar_auth() converts function input to nectar_auth (#81)", {
+  test_result <- .as_nectar_auth(req_auth_api_key)
+  expect_s3_class(test_result, "nectar_auth")
+  expect_identical(test_result$auth_fn, req_auth_api_key)
+  expect_identical(test_result$auth_args, list())
+})
+
+test_that(".as_nectar_auth() merges auth_args with additional auth fields (#81)", {
+  test_result <- .as_nectar_auth(list(
+    auth_fn = req_auth_api_key,
+    auth_args = list(parameter_name = "parm"),
+    api_key = "my_key",
+    location = "query"
+  ))
+  expect_s3_class(test_result, "nectar_auth")
+  expect_identical(
+    test_result$auth_args,
+    list(parameter_name = "parm", api_key = "my_key", location = "query")
+  )
+})
+
+test_that(".as_nectar_auth() errors for non-listable auth_args (#81)", {
+  stbl::expect_pkg_error_classes(
+    .as_nectar_auth(list(auth_fn = req_auth_api_key, auth_args = mean)),
+    "stbl",
+    class = "bad_function"
+  )
+})
diff --git a/tests/testthat/test-req_auth_api_key.R b/tests/testthat/test-req_auth_api_key.R
index 31d7145..03e00aa 100644
--- a/tests/testthat/test-req_auth_api_key.R
+++ b/tests/testthat/test-req_auth_api_key.R
@@ -12,6 +12,20 @@ test_that("req_auth_api_key errors informatively with unused arguments", {
   )
 })
 
+test_that("auth_api_key() prepares req_auth_api_key auth (#81)", {
+  test_result <- auth_api_key(
+    parameter_name = "parm",
+    api_key = "my_key",
+    location = "query"
+  )
+  expect_s3_class(test_result, "nectar_auth")
+  expect_identical(test_result$auth_fn, req_auth_api_key)
+  expect_identical(
+    test_result$auth_args[c("parameter_name", "api_key", "location")],
+    list(parameter_name = "parm", api_key = "my_key", location = "query")
+  )
+})
+
 test_that("req_auth_api_key returns req unchanged if api_key is NA or empty (#76)", {
   req <- httr2::request("https://example.com")
   expect_identical(req, req_auth_api_key(req, "parm", api_key = NA_character_))
diff --git a/tests/testthat/test-req_prepare.R b/tests/testthat/test-req_prepare.R
index bde0bfd..189f295 100644
--- a/tests/testthat/test-req_prepare.R
+++ b/tests/testthat/test-req_prepare.R
@@ -153,6 +153,27 @@ test_that("req_prepare() applies tidying", {
   )
 })
 
+test_that("req_prepare() applies prepared auth (#81)", {
+  test_result <- req_prepare(
+    base_url = "https://example.com",
+    auth = auth_prepare(req_auth_api_key, "parm", api_key = "my_key")
+  )
+  expect_in(
+    "parm",
+    names(test_result$headers)
+  )
+})
+
+test_that("req_prepare() errors for unsupported auth objects (#81)", {
+  expect_error(
+    req_prepare(
+      base_url = "https://example.com",
+      auth = "not_auth"
+    ),
+    class = "nectar-error-unsupported_auth_class"
+  )
+})
+
 test_that(".as_nectar_request() fails gracefully for non-reqs", {
   test_obj <- 1
   expect_nectar_error_snapshot(
diff --git a/vignettes/nectar.Rmd b/vignettes/nectar.Rmd
index ff90426..85d8231 100644
--- a/vignettes/nectar.Rmd
+++ b/vignettes/nectar.Rmd
@@ -27,9 +27,9 @@ The main entry point in nectar is `req_prepare()`. It wraps `httr2::request()` a
 Here we prepare a request to the Crossref `/works` endpoint. We ask for ten results per page (`rows = 10`), select only the "publisher" and "DOI" fields, tell `{httr2}` to concatenate the `select` parameter with commas (`.multi`), and set the `cursor` parameter to `"*"` to trigger cursor-based pagination:
 
 
-## Authentication with `req_auth_api_key()`
+## Authentication with `auth_api_key()`
 
-Many APIs accept an optional key (or, as in Crossref's case, an email address) to identify your application and gain access to a higher rate limit. nectar provides `req_auth_api_key()` for this purpose. You can pass it through `req_prepare()` via the `auth_fn` and `auth_args` arguments:
+Many APIs accept an optional key (or, as in Crossref's case, an email address) to identify your application and gain access to a higher rate limit. nectar provides `auth_api_key()` to prepare this authentication and pass it through `req_prepare()` via the `auth` argument:
 
 ```{r auth, eval = FALSE}
 req <- req_prepare(
@@ -37,8 +37,7 @@ req <- req_prepare(
   query = list(
     rows = 10, cursor = "*", select = c("publisher", "DOI"), .multi = "comma"
   ),
-  auth_fn = req_auth_api_key,
-  auth_args = list("mailto", api_key = "your@email.com", location = "query")
+  auth = auth_api_key("mailto", api_key = "your@email.com", location = "query")
 )
 ```
 
@@ -171,8 +170,7 @@ works <- function(
   req_prepare(
     "https://api.crossref.org/works",
     query = list(rows = rows, cursor = "*", select = select),
-    auth_fn = req_auth_api_key,
-    auth_args = list("mailto", api_key = mailto, location = "query"),
+    auth = auth_api_key("mailto", api_key = mailto, location = "query"),
     tidy_fn = resp_tidy_json,
     tidy_args = list(subset_path = c("message", "items")),
     pagination_fn = iterate_with_json_cursor(