chore: regens API reference docs (#889)

diff --git a/docs/dyn/iamcredentials_v1.projects.serviceAccounts.html b/docs/dyn/iamcredentials_v1.projects.serviceAccounts.html
index a020611..b279466 100644
--- a/docs/dyn/iamcredentials_v1.projects.serviceAccounts.html
+++ b/docs/dyn/iamcredentials_v1.projects.serviceAccounts.html
@@ -75,31 +75,28 @@
 <h1><a href="iamcredentials_v1.html">IAM Service Account Credentials API</a> . <a href="iamcredentials_v1.projects.html">projects</a> . <a href="iamcredentials_v1.projects.serviceAccounts.html">serviceAccounts</a></h1>
 <h2>Instance Methods</h2>
 <p class="toc_element">
-  <code><a href="#generateAccessToken">generateAccessToken(name, body, x__xgafv=None)</a></code></p>
+  <code><a href="#generateAccessToken">generateAccessToken(name, body=None, x__xgafv=None)</a></code></p>
 <p class="firstline">Generates an OAuth 2.0 access token for a service account.</p>
 <p class="toc_element">
-  <code><a href="#generateIdToken">generateIdToken(name, body, x__xgafv=None)</a></code></p>
+  <code><a href="#generateIdToken">generateIdToken(name, body=None, x__xgafv=None)</a></code></p>
 <p class="firstline">Generates an OpenID Connect ID token for a service account.</p>
 <p class="toc_element">
-  <code><a href="#generateIdentityBindingAccessToken">generateIdentityBindingAccessToken(name, body, x__xgafv=None)</a></code></p>
-<p class="firstline"></p>
-<p class="toc_element">
-  <code><a href="#signBlob">signBlob(name, body, x__xgafv=None)</a></code></p>
+  <code><a href="#signBlob">signBlob(name, body=None, x__xgafv=None)</a></code></p>
 <p class="firstline">Signs a blob using a service account's system-managed private key.</p>
 <p class="toc_element">
-  <code><a href="#signJwt">signJwt(name, body, x__xgafv=None)</a></code></p>
+  <code><a href="#signJwt">signJwt(name, body=None, x__xgafv=None)</a></code></p>
 <p class="firstline">Signs a JWT using a service account's system-managed private key.</p>
 <h3>Method Details</h3>
 <div class="method">
-    <code class="details" id="generateAccessToken">generateAccessToken(name, body, x__xgafv=None)</code>
+    <code class="details" id="generateAccessToken">generateAccessToken(name, body=None, x__xgafv=None)</code>
   <pre>Generates an OAuth 2.0 access token for a service account.
 
 Args:
-  name: string, The resource name of the service account for which the credentials
+  name: string, Required. The resource name of the service account for which the credentials
 are requested, in the following format:
 `projects/-/serviceAccounts/{ACCOUNT_EMAIL_OR_UNIQUEID}`. The `-` wildcard
 character is required; replacing it with a project ID is invalid. (required)
-  body: object, The request body. (required)
+  body: object, The request body.
     The object takes the form of:
 
 {
@@ -119,7 +116,7 @@
         # character is required; replacing it with a project ID is invalid.
       "A String",
     ],
-    "scope": [ # Code to identify the scopes to be included in the OAuth 2.0 access token.
+    "scope": [ # Required. Code to identify the scopes to be included in the OAuth 2.0 access token.
         # See https://developers.google.com/identity/protocols/googlescopes for more
         # information.
         # At least one value required.
@@ -143,21 +140,21 @@
 </div>
 
 <div class="method">
-    <code class="details" id="generateIdToken">generateIdToken(name, body, x__xgafv=None)</code>
+    <code class="details" id="generateIdToken">generateIdToken(name, body=None, x__xgafv=None)</code>
   <pre>Generates an OpenID Connect ID token for a service account.
 
 Args:
-  name: string, The resource name of the service account for which the credentials
+  name: string, Required. The resource name of the service account for which the credentials
 are requested, in the following format:
 `projects/-/serviceAccounts/{ACCOUNT_EMAIL_OR_UNIQUEID}`. The `-` wildcard
 character is required; replacing it with a project ID is invalid. (required)
-  body: object, The request body. (required)
+  body: object, The request body.
     The object takes the form of:
 
 {
     "includeEmail": True or False, # Include the service account email in the token. If set to `true`, the
         # token will contain `email` and `email_verified` claims.
-    "audience": "A String", # The audience for the token, such as the API or account that this token
+    "audience": "A String", # Required. The audience for the token, such as the API or account that this token
         # grants access to.
     "delegates": [ # The sequence of service accounts in a delegation chain. Each service
         # account must be granted the `roles/iam.serviceAccountTokenCreator` role
@@ -187,101 +184,19 @@
 </div>
 
 <div class="method">
-    <code class="details" id="generateIdentityBindingAccessToken">generateIdentityBindingAccessToken(name, body, x__xgafv=None)</code>
-  <pre>
-
-Args:
-  name: string, The resource name of the service account for which the credentials
-are requested, in the following format:
-`projects/-/serviceAccounts/{ACCOUNT_EMAIL_OR_UNIQUEID}`. The `-` wildcard
-character is required; replacing it with a project ID is invalid. (required)
-  body: object, The request body. (required)
-    The object takes the form of:
-
-{
-    "scope": [ # Code to identify the scopes to be included in the OAuth 2.0 access token.
-        # See https://developers.google.com/identity/protocols/googlescopes for more
-        # information.
-        # At least one value required.
-      "A String",
-    ],
-    "jwt": "A String", # Required. Input token.
-        # Must be in JWT format according to
-        # RFC7523 (https://tools.ietf.org/html/rfc7523)
-        # and must have 'kid' field in the header.
-        # Supported signing algorithms: RS256 (RS512, ES256, ES512 coming soon).
-        # Mandatory payload fields (along the lines of RFC 7523, section 3):
-        # - iss: issuer of the token. Must provide a discovery document at
-        #        $iss/.well-known/openid-configuration . The document needs to be
-        #        formatted according to section 4.2 of the OpenID Connect Discovery
-        #        1.0 specification.
-        # - iat: Issue time in seconds since epoch. Must be in the past.
-        # - exp: Expiration time in seconds since epoch. Must be less than 48 hours
-        #        after iat. We recommend to create tokens that last shorter than 6
-        #        hours to improve security unless business reasons mandate longer
-        #        expiration times. Shorter token lifetimes are generally more secure
-        #        since tokens that have been exfiltrated by attackers can be used for
-        #        a shorter time. you can configure the maximum lifetime of the
-        #        incoming token in the configuration of the mapper.
-        #        The resulting Google token will expire within an hour or at "exp",
-        #        whichever is earlier.
-        # - sub: JWT subject, identity asserted in the JWT.
-        # - aud: Configured in the mapper policy. By default the service account
-        #        email.
-        # 
-        # Claims from the incoming token can be transferred into the output token
-        # accoding to the mapper configuration. The outgoing claim size is limited.
-        # Outgoing claims size must be less than 4kB serialized as JSON without
-        # whitespace.
-        # 
-        # Example header:
-        # {
-        #   "alg": "RS256",
-        #   "kid": "92a4265e14ab04d4d228a48d10d4ca31610936f8"
-        # }
-        # Example payload:
-        # {
-        #   "iss": "https://accounts.google.com",
-        #   "iat": 1517963104,
-        #   "exp": 1517966704,
-        #   "aud":
-        #   "https://iamcredentials.googleapis.com/google.iam.credentials.v1.CloudGaia",
-        #   "sub": "113475438248934895348",
-        #   "my_claims": {
-        #     "additional_claim": "value"
-        #   }
-        # }
-  }
-
-  x__xgafv: string, V1 error format.
-    Allowed values
-      1 - v1 error format
-      2 - v2 error format
-
-Returns:
-  An object of the form:
-
-    {
-    "expireTime": "A String", # Token expiration time.
-        # The expiration time is always set.
-    "accessToken": "A String", # The OAuth 2.0 access token.
-  }</pre>
-</div>
-
-<div class="method">
-    <code class="details" id="signBlob">signBlob(name, body, x__xgafv=None)</code>
+    <code class="details" id="signBlob">signBlob(name, body=None, x__xgafv=None)</code>
   <pre>Signs a blob using a service account's system-managed private key.
 
 Args:
-  name: string, The resource name of the service account for which the credentials
+  name: string, Required. The resource name of the service account for which the credentials
 are requested, in the following format:
 `projects/-/serviceAccounts/{ACCOUNT_EMAIL_OR_UNIQUEID}`. The `-` wildcard
 character is required; replacing it with a project ID is invalid. (required)
-  body: object, The request body. (required)
+  body: object, The request body.
     The object takes the form of:
 
 {
-    "payload": "A String", # The bytes to sign.
+    "payload": "A String", # Required. The bytes to sign.
     "delegates": [ # The sequence of service accounts in a delegation chain. Each service
         # account must be granted the `roles/iam.serviceAccountTokenCreator` role
         # on its next service account in the chain. The last service account in the
@@ -305,25 +220,29 @@
   An object of the form:
 
     {
-    "signedBlob": "A String", # The signed blob.
+    "signedBlob": "A String", # The signature for the blob. Does not include the original blob.
     "keyId": "A String", # The ID of the key used to sign the blob.
   }</pre>
 </div>
 
 <div class="method">
-    <code class="details" id="signJwt">signJwt(name, body, x__xgafv=None)</code>
+    <code class="details" id="signJwt">signJwt(name, body=None, x__xgafv=None)</code>
   <pre>Signs a JWT using a service account's system-managed private key.
 
 Args:
-  name: string, The resource name of the service account for which the credentials
+  name: string, Required. The resource name of the service account for which the credentials
 are requested, in the following format:
 `projects/-/serviceAccounts/{ACCOUNT_EMAIL_OR_UNIQUEID}`. The `-` wildcard
 character is required; replacing it with a project ID is invalid. (required)
-  body: object, The request body. (required)
+  body: object, The request body.
     The object takes the form of:
 
 {
-    "payload": "A String", # The JWT payload to sign: a JSON object that contains a JWT Claims Set.
+    "payload": "A String", # Required. The JWT payload to sign. Must be a serialized JSON object that contains a
+        # JWT Claim Set. For example: `{"sub": "user@example.com", "iat": 313435}`
+        # 
+        # If the claim set contains an `exp` claim, it must be an integer timestamp
+        # that is not in the past and at most 12 hours in the future.
     "delegates": [ # The sequence of service accounts in a delegation chain. Each service
         # account must be granted the `roles/iam.serviceAccountTokenCreator` role
         # on its next service account in the chain. The last service account in the
@@ -348,7 +267,9 @@
 
     {
     "keyId": "A String", # The ID of the key used to sign the JWT.
-    "signedJwt": "A String", # The signed JWT.
+    "signedJwt": "A String", # The signed JWT. Contains the automatically generated header; the
+        # client-supplied payload; and the signature, which is generated using the
+        # key referenced by the `kid` field in the header.
   }</pre>
 </div>