diff --git a/api/client-server/v1/login.yaml b/api/client-server/v1/login.yaml
index 2df695bee..3d415c293 100644
--- a/api/client-server/v1/login.yaml
+++ b/api/client-server/v1/login.yaml
@@ -29,7 +29,6 @@ paths:
       parameters:
         - in: body
           name: body
-          required: true
           schema:
             type: object
             example: |-
@@ -63,7 +62,19 @@ paths:
                 description: The fully-qualified Matrix ID that has been registered.
               access_token:
                 type: string
-                description: An access token for the account. This access token can then be used to authorize other requests.
+                description: |-
+                  An access token for the account.
+                  This access token can then be used to authorize other requests.
+                  The access token may expire at some point, and if so, it SHOULD come with a ``refresh_token``.
+                  There is no specific error message to indicate that a request has failed because
+                  an access token has expired; instead, if a client has reason to believe its
+                  access token is valid, and it receives an auth error, they should attempt to
+                  refresh for a new token on failure, and retry the request with the new token.
+              refresh_token:
+                type: string
+                # TODO: Work out how to linkify /tokenrefresh
+                description: |-
+                  (optional) A ``refresh_token`` may be exchanged for a new ``access_token`` using the /tokenrefresh API endpoint.
               home_server:
                 type: string
                 description: The hostname of the Home Server on which the account has been registered.
@@ -77,3 +88,60 @@ paths:
           description: This request was rate-limited.
           schema:
             "$ref": "definitions/error.yaml"
+  "/tokenrefresh":
+    post:
+      summary: Exchanges a refresh token for an access token.
+      description: |-
+        Exchanges a refresh token for a new access token.
+        This is intended to be used if the access token has expired.
+      security:
+        - accessToken: []
+      parameters:
+        - in: body
+          name: body
+          schema:
+            type: object
+            example: |-
+              {
+                "refresh_token": "a1b2c3"
+              }
+            properties:
+              refresh_token:
+                type: string
+                description: The refresh token which was issued by the server.
+            required: ["refresh_token"]
+      responses:
+        200:
+          description: |-
+            The refresh token was accepted, and a new access token has been issued.
+            The passed refresh token is no longer valid and cannot be used.
+            A new refresh token will have been returned unless some policy does
+            not allow the user to continue to renew their session.
+          examples:
+            application/json: |-
+              {
+                "access_token": "bearwithme123",
+                "refresh_token": "exchangewithme987"
+              }
+          schema:
+            type: object
+            properties:
+              access_token:
+                type: string
+                description: |-
+                  An access token for the account.
+                  This access token can then be used to authorize other requests.
+                  The access token may expire at some point, and if so, it SHOULD come with a ``refresh_token``.
+              refresh_token:
+                type: string
+                description: (optional) A ``refresh_token`` may be exchanged for a new ``access_token`` using the TODO Linkify /tokenrefresh API endpoint.
+        403:
+          description: |-
+            The exchange attempt failed. For example, the refresh token may have already been used.
+          examples:
+            application/json: |-
+              {"errcode": "M_FORBIDDEN"}
+        429:
+          description: This request was rate-limited.
+          schema:
+            "$ref": "definitions/error.yaml"
diff --git a/drafts/macaroons_caveats.rst b/drafts/macaroons_caveats.rst
new file mode 100644
index 000000000..93622c3d4
--- /dev/null
+++ b/drafts/macaroons_caveats.rst
@@ -0,0 +1,34 @@
+Macaroon Caveats
+================
+
+`Macaroons`_ are issued by Matrix servers as authorization tokens. Macaroons may be restricted by adding caveats to them.
+
+.. _Macaroons: http://theory.stanford.edu/~ataly/Papers/macaroons.pdf
+
+Caveats can only be used for reducing the scope of a token, never for increasing it. Servers are required to reject any macroon with a caveat that they do not understand.
+
+Some caveats are specified in this specification, and must be understood by all servers. The use of non-standard caveats is allowed.
+
+All caveats must take the form:
+
+`key` `operator` `value`
+where `key` is a non-empty string drawn from the character set [A-Za-z0-9_]
+`operator` is a non-empty string which does not contain whitespace
+`value` is a non-empty string
+And these are joined by single space characters.
+
+Specified caveats:
+
++-------------+--------------------------------------------------+------------------------------------------------------------------------------------------------+
+| Caveat name | Description                                      | Legal Values                                                                                   |
++-------------+--------------------------------------------------+------------------------------------------------------------------------------------------------+
+| gen         | Generation of the macaroon caveat spec.          | 1                                                                                              |
+| user_id     | ID of the user for which this macaroon is valid. | Pure equality check. Operator must be =.                                                       |
+| type        | The purpose of this macaroon.                    | access - used to authorize any action except token refresh                                     |
+|                                                                   refresh - only used to authorize a token refresh                                              |
+| time        | Time before/after which this macaroon is valid.  | A POSIX timestamp in milliseconds (in UTC).                                                    |
+|                                                                  Operator < means the macaroon is valid before the timestamp, as interpreted by the server.     |
+|                                                                  Operator > means the macaroon is valid after the timestamp, as interpreted by the server.      |
+|                                                                  Operator == means the macaroon is valid at exactly the timestamp, as interpreted by the server.|
+|                                                                  Note that exact equality of time is largely meaningless.                                       |
++-------------+--------------------------------------------------+------------------------------------------------------------------------------------------------+